So I spent a few nights with the Mistress... and I've had a fantastic time.
In this review, I'll be discussing her features as well as juxtaposing some of them against the popular Boss BF-2 Flanger (which I used to own) and my ever-faithful EHX Clone Theory (my current favorite chorus). DIGITAL? Yes, it's digital - EHX confirmed it. And don't let that stop you - it's true bypass and absolutely awesome!
POWER: 9VDC, 2.1mm center-negative DC jack.
She uses your ordinary 9VDC Boss-style adapter. She conveniently comes with her own adapter, too, but for a good reason:
she doesn't run on batteries. My advice? Use a daisy chain or brick - she's friendly with all the usual suspects.
CONTROLS: Like the other XO series pedals, she has
three knobs to play with (
):
Rate, Flanger Depth, and Chorus Depth.
I find it interesting that EHX opted to not use a toggle switch for the Filter Matrix mode (they used a switch on the XO Stereo Pulsar and the XO Octave Multiplexer, not surprisingly). Instead,
activating Filter Matrix mode requires you to keep the Rate knob between the minimum setting and 10:00. Above 10:00 is the switch point: it takes you into the lowest rate settings of the normal flanging/chorus mode. The switch point is not detented, but it's not an issue - the LED and the difference in sound will tell you that you've switched.
LED: The LED on the Mistress is awesome! I know you guys are always talking about blue LEDs being superior, but these "headlights" are worth taking a look at!
It changes colors from bright yellow (with a hint of lime) to bright red (on the verge of hot pink). Its color and behavior vary depending on how you're using the pedal.
In Filter Matrix mode, the LED does not shift; it's fixed on a particular color that reflects the part of the flanger sweep you're honing in on. This provides a visual guide to remembering your favorite position in the Filter Matrix; in fact, if you find a section of the sweep that you love when in normal mode, just remember its color at the moment you heard that part, and dial that color in Filter Matrix mode.
When in normal mode, the LED will cycle colors at a speed according to the Rate setting; it cycles through the colors faster as the Rate increases, again giving you a visual guide to your settings. 
SOUND (FLANGER): I'll be honest; I didn't think I was going to be all that fond of her before she arrived. In that ever-constant phaser vs. flanger debate, I have typically been more of a "phase shifter guy."
This pedal has definitely changed my mind about flanging - maybe it was her looks, or her voice, or her personality... regardless,
I can call myself a "flanger guy" now! The Electric Mistress was always famous for her dramatic sweeps and her Filter Matrix mode; both elements are still present in her new package, and after listening to clips of the originals on guitar, I can say that she seems to stay true to the Mistress legacy (whether or not she matches exactly is a subjective issue that I'm not qualified to comment on).
With the Flanger Depth at minimum, your tone is practically unaltered;
it's surprising that an effect this wild doesn't destroy the natural tone of your bass (unless you're using Filter Matrix mode).
The flanging effect overall is distinctly metallic, but somehow natural feeling; unlike the BF-2, it doesn't "dry out" your tone. It certainly has that EHX warmth and "mojo".
With the Flanger Depth at low settings, it can be mellow, less metallic, less pronounced - perfect for quiet passages and slap bass jams.
When cranked, it's definitive and ever-present but not overbearing on your notes; your playing still shines through, and it isn't drowned about by the flanging. It's more complimentary than the BF-2 to your natural tone. Her voice musical and hypnotic, like the song of a Siren.
When Filter Matrix mode is on, it's a different story; this is where the bizarre, unforgiving stuff comes in. Depending on your Flanger Depth and Rate settings, you can get some subtle harmonic emphasis, or some really creepy metallic chime effects. As you adjust the rate, it focuses on a different part of the sweep, and retains the harmonics you would hear in that portion of the sweep. Subtle tweaks in the knob will make a significant difference. You can dial it in to better compliment your overdrive/distortion/fuzz pedal, or go against the grain for some really unusual ear-shattering rings. Filter Matrix mode is the dark side of the Mistress - like the shriek of a Siren after she's lured you in. It kinda makes you want to tie your TV down so she can't throw it out the third floor window.
SOUND (CHORUS): After A/B'ing it with the Clone Theory, I can definitely say that these two chorus effects are significantly different from each other. The Clone Theory is bright, articulate, and capable of crazy stuff;
the chorus on the Mistress is more laid-back, less extreme, and a bit warmer, but still has a pleasant amount of lushness. It's actually really nice alone, but you can tell its delay time is more akin to a flanger because of how the chorus sounds; on some Rate/Depth setting combinations, it's a warm chorus, and on others, it feels more "liquidy", like a mild flanger working to be a chorus. I'll still be working with both chorus pedals for a while to see which I prefer, but there's a possibility that I might keep both...
SOUND (COMBINED): Thicker, lusher, more inviting flanging effects, with the presence of chorus detuning. It's definitely seduced me. The flanging seems more ambient and pronounced when you mix the two, but what you're really hearing are two signals blended together - one chorus, one flanger. If you listen carefully, you can hear the flanger sweeps are not being modulated by the chorus.
According to EHX, the Mistress has both effects in parallel, so yes - they're blended, and very well, I might add! 
NOISE: Surprisingly, there's barely any noise at all with this pedal - no hum, no hiss, only some very slight residual flanging at high volumes. IMO, it's so minor, it's unnoticeable in a band setting, and I don't see how it could possibly hamper a recording. For the record, a pedal like the Boss BF-2 is far worse in this department. It's nice to know that she's quiet when I want her to be.
STEREO MODE: It was a real joy to test her out in stereo. Similar to the Pulsar, the Mistress cycles the flanger sweep between the two outputs;
it's as if your sound is literally swirling around you. This pedal sounds great in mono, but stereo is what really makes the Mistress sexy!
PROBLEMS: Other than the fact that you can't use batteries... I don't really see any problems. I guess the chorus could have been "better" (IMO), but it's still great when used alone, and more importantly, it's an excellent compliment to her most outstanding features.
SUMMARY:
A true treasure in Electro-Harmonix's latest line of reissues, I am still surprised by how amazing the she sounds on my bass for having so few controls available.
If you leave your other flanger for her, I don't blame you! RATING: 
SOUND CLIPS: I know you guys have been waiting for these. Enjoy!
Random Flanger Demos - A series of demos recorded using my MM Stingray and the preamp of my 2001RB, direct to my computer's soundcard. All parts of this track are various settings of the normal flanger section only. IMO, the two best samples are at the end - one's done in pickstyle using my favorite setting so far, the other is fingerstyle. The rest of the clip is pickstyle, though.
Filter Matrix Demos - This one's a sample of a few tones from the Filter Matrix section of the EHX Stereo Electric Mistress. Recorded the same way the last one was.
Chorus + Flanger Combo - In this clip, I turn up both the chorus and flanger in the Stereo Electric Mistress to show you how cool the two can be when combined. How it's combining them, I'm not sure. You might recognize the riff I'm playing if you're a Tool fan. You might also be mad that I couldn't play it well. Give me a break - I learned it for the first time just a few minutes ago!
I felt it'd be appropriate for this demo.
EHX Clone Theory (Chorus) Versus EHX Electric Mistress (Chorus) - This one pits the Clone Theory and the Electric Mistress head-to-head. The first half is the Clone Theory on a high depth, low rate setting. The second half is the Mistress on a high depth, low rate setting. You can easily hear the differences. The former is bright, articulate, and proud of its top end. The latter is more liquid-like and smooth, and dead silent in the noise department.
EHX Stereo Electric Mistress Review - SOUND CLIPS ADDED! 
