I have experienced venting in two mech mods over the past 3 years.. I believe Baditude had a batt vent in one of his.. It does happen. Says everything for the ProVari and other safe, regulated voltage / power devices.. The battery is constantly being monitored. Personally, I think anyone who does not at least run a fuse in a mech is foolish..
This is 2014.. We used mechs a few years ago because that's all we had until the Buzz and ProVari came on the scene. I own and like mechs for reasons I posted before, but I use them with Kick 2's. I have a DNA 30 device just in case I do get the itch to go more extreme with my builds.

With the many high wattage devices now here, and more coming, mechs in general will be a relic of the past before too long IMO..