That MXR BEF is a very nice pedal but there are a few tricks it definitely can't do and others can.
Band Frequencies: You are right that there are multiple such passes that control which frequencies are affected by the envelope filter. If you have ever seen a live visualizer for an EQ you can see this happening in real time. A Low Pass filter lets all lows pass below a cutoff frequency (best bass response), a High Pass filter lets all highs pass above a cutoff frequency (sharpest sound), and a Band Pass filter only lets a small band of frequencies pass above a low cutoff frequency and below a high cutoff frequency. Simply put, the classic envelope filter for bass is a Low Pass filter. A Wah-wah pedal is almost always a Band Pass filter. A High Pass filter gets you the most quack. Some filters give you more of these as options. Example: Maxon Auto Filter, Fender Pour Over Filter
Envelope control: The path of an envelope is (generally) Attack, Decay, Sustain, Release. This is sometimes called an ADSR filter. In simple terms, attack is how fast the signal moves from the start frequency of the filter to the stop frequency. Decay is how fast the signal moves from the stop frequency to the sustain frequency. Sustain is what happens when you hold the note, and generally how long it remains at that frequency before the Release, which is how fast the signal returns to the Start frequency. The BEF simplifies this by giving you a Decay control. Other filters have more or less control of these and sometimes the knobs for them are labeled different things (or combine functionality). Example: the EHX Enigma has Attack and Decay knobs that change the speed the filter reaches the Start and Stop positions, that you can also control. When a filter has an UP or DOWN option (e.g. Chunk Systems Agent 00 Funk), what this means is that it flips the Start and Stop positions so you are going from a higher frequency to a lower one instead of only a lower frequency to a higher one.
Effects loop: Some envelope filters let you stick effects in a loop which triggers when the Attack part of the filter is engaged. So now when the envelope "opens up" in the above ADSR pattern, another effect is happening at the same time. Classic applications here are a fuzz because you feel the envelope opening and closing around your fuzzy notes which would sound much less dynamic if the fuzz was just after the filter. If it were before, obviously it may change how well the envelope filter responds to your playing dynamics at all. Example: EHX Q-Tron Plus, Lovetone Meatball
Oscillators: The opposite of an envelope filter, an oscillator predictably raises and lowers the frequency of the signal automatically. So rather than play an envelope filter, you're playing through a more synthesizer-like modulated filter. It's kind of like turning a filter into something that feels more like a phaser. Example: Dr. Scientist Dusk, WMD Super Fatman
Expression Pedals: Some envelope filters let you plug in an expression pedal to manually control the path from the Start (heel) to the Stop (toe) frequency. If the filter has a band pass option, then you can make it into a classic wah-wah effect with much more control over the sound than a typical wah. Example: Subdecay Prometheus DLX, EHX Enigma
Distortion/Fuzz: For convenience and coolness, some filters have a fuzz ready to go within it, saving you the trouble of putting one in an effects loop. Example: Fuzzrocious Croak, EHX Bassballs, West Co Grease Juicer
That's not intended to be an exhaustive list but it should be helpful. Filters are one of the coolest effects and I love trying new ones. I think the biggest thing that makes someone love or hate a filter is how it responds to your playing. I think the magic of filters is partly that everyone plays a little different and some work better than others for how you play no matter how expensive or how good a pedigree a filter has. For my money, I have used the EHX Enigma for years and it's my favorite filter. It is a bigger enclosure and has a learning curve to use but it covers a ton of ground.
