My understanding is that it's a bit of both, last I looked at them they have a low-voltage cut-off as well as the VV/VW features, so they should in theory keep you from over-draining a battery in a mech
mod. Whether they have fuse circuitry for short-circuit protection, I don't know, but I believe they have a resistance limit around 1.4ohms or something, so that should do the same thing. Of course they also keep you from using sub-ohm
coils which is the biggest reason to run a mech for most people.
They should work in non-telescoping mods, an 18500 and a Kick should be the same length as a 18650, and an 18350 and Kick would approximate an 18500.