Can anyone who has used both a Turbo Tuner and a Pitchblack comment on the differences between the two?
Any specific questions? I have a Turbo Tuner (ST-200) and a PitchBlack+ (PB02) and often use both of them at the same time. My Pitchblack+ is used as an A/B switch and "muted" tuner, and I run the TurboTuner from my amp's tuner output for "always on" tuning status.
NOTE: keep in mind that I'm talking about the PBO2/PitchBlack+, not the single channel PitchBlack. According to the specs from Korg, the PB+ is a bit more accurate (+/-0.1 cent) than the PitchBlack (+/- 1 cent).
One issue with both of these is that they are true bypass, which is both good (no change to your signal when you're not tuning) and bad (can't see tuning and pass signal through at the same time). It would be nice to have the option of tuning and passing the signal through at the same time, but then you lose true bypass. I think some of the Peterson tuners can be configured to do that (and I'm not 100% certain the PitchBlack+ can't be, just haven't tried yet). This is why I tend to use both at once - I need to mute while tuning, but I also like to check while I'm playing.
Both of them seem quite accurate and far more sensitive than other tuners I've used (most recently the tuners in the GT-10B and the TC-RH450). I think the TurboTuner locks in a little faster, but it's not a huge difference. And the TurboTuner might be more accurate, but the PitchBlack is still very, very capable of splitting sonic hairs...
These things measure with enough precision that it can be frustrating to get in "perfect" tune. On an open string, I see changes in pitch based on technique (how the note is played) and as the note decays. For checking intonation, both show a noticeable swing based on the pressure you use to fret the string. I can easily see repeatable patterns which are too subtle for my ears to catch. So if you tend to get a bit OCD, these might actually be too precise... OTOH, it's kinda cool to measure the impact your playing style has on pitch even with a fretted bass.
The display on the PitchBlack+ is (IMHO) a bit easier to read. However, part of this is because the TurboTuner doesn't "average" a complex signal, it just displays it with warts and all. So if you hit a string with a bit of fret buzz or harmonics, that will affect the visual output on the TurboTuner - even if it shows the same pitch (strobe rotation rate), you can see differences in "texture". This might add to the usable accuracy, because I suspect your eyes are better at picking out the strobe pattern on complex tones than any (currently affordable in a tuner) circuit or algorithm trying to average it down to a specific pitch.
One other minor issue: neither directly support Buzz Feiten tuning, but both can be set up for several "custom" tunings so that is probably not a huge deal. I haven't bothered because while I have a six string MTD (supposedly all MTD basses use Buzz Feiten tuning), it's fretless, so I'm not quite sure how or if that matters.