Well, for example...
Fenders generally use 250K ohm volume pots on single coils
Gibson was using 500K ohm pots on humbuckers
EMG uses 25K ohm volume pots, thus the idea that active = 25K ohms
I suspect that the theory of offering two pedals is that it is most effective when it matches what is on your guitar.
Check out this page for some useful info:
http://www.blueguitar.org/new/schem/_gtr/gtr_wiring-stewmac.pdf What I don't know is the spec for an Alembic volume pot.
From what I think I comprehend of the research I just did, if you're using the pedal mostly for on/off, I'd go with the higher number anyway. If you're trying to fine-tune your volume, you may have more flexibility with the active pedal if your guitar uses a 25K ohm volume pot.