Like I said above, passive LPGs have a minimum voltage threshold on the CV before they open. For instance, at 0.83 volts the LPG might be silent, but at 0.84 volts it suddenly lets some audio pass through. It sounds odd if you try to use it with a slow attack envelope; it’s not a problem with faster attacks or if you just “ping” it with a trigger.
Passive LPGs do sometimes have unusual side effects with some CV sources – for instance, Befaco Rampage will “freeze” in its cycle and keep the LPG open. You can avoid that with a buffered mult or an attenuator.
Also, resonant filters require active electronics for amplification. A lot of LPG designs aren’t resonant anyway, but a few are. It’s not so much a case of “passive LPGs sound different from active LPGs” in a general sense though. I think the DPLPG (passive) sounds more like the Sputnik Quad VCF/VCA (active) than it does the Mystic Circuits 0HP LPG (passive) or Schenk.Werk Gerridae (passive).
It’s a specific module by Rabid Elephant. Relatively expensive and a little hard to get a hold of due to production issues, though they seem to be solving that. Instead of vactrols it has its own internal envelope circuits, with adjustable and CVable lengths, and a mode switches that affects the attack and decay curves and the frequency response. It’s very hands-on and playable, and to me it also sounds a little bit nicer than my other favorite LPGs.