I retired my two mechs a couple of years ago. I came to the conclusion that I get a better vape from my regulated mods because I can change my vape "on the fly" (you can't do that with a mech). I was also concerned about the lack of protection circuitry on a mech (I had a battery explode in my first mech several years ago). You can be obsessive compulsive about battery safety, but it would only take one careless moment to result in a catastrophe.
You don't want to end up like this poor guy:
First vape related death . He was using a mech that had inadequate ventilation. He had a battery vent gas into his mech which turned it into a pipe bomb, which propelled his atomizer into his skull.
If you look at images of mech mods which exploded (Google Image it), nearly all of them blow their tops off.
So my advice is your first priority should be looking for
adequate ventilation holes should a battery vent. Batteries are designed to vent gas from their positive pole in order to prevent the cell from exploding. If a metal tube mech doesn't have vent holes to allow the gas to escape the tube, it essentially becomes a pipe bomb.
Ideally the vent holes should be located where the positive pole of the battery will be oriented. Batteries venting or going into thermal runaway can swell in size, effectively blocking the passageway to vent holes located at the other end of the tube.
Mech Mods with top venting holes?
Other things to look for would be a
locking fire button (in case you carry your mod in your pocket), or
at least a recessed fire button. You don't want your mod to fire accidentally in your pocket.
I'm always on the lookout for a mech that has simple and basic safety designs that I could recommend. I haven't found one yet.