The only safety concerns I can see with mechs clones or authentic are the following (not including battery safety)
1. Hybrid connectors: direct connection between your topper and the battery..you need to make sure your 510 pin is hitting the battery and battery does not hit metal on top cap
2. Firing button, lot of mods tend to use cheap springs...it can collapse under intense use (super sub-ohm). So if there is magnet option or really good quality spring...definitely upgrade to it.
3. bad threading on tubes, firing connector..can auto fire, if you hit the wrong way..button can get stuck and continuously to fire
4. Lazyitiness....it's disease among few mech mod users...they treat them like regulated device and not clean them properly...washing the tubes, drying them, adjusting the firing ping, cleaning the contacts etc is necessary....
I heard that Fasttech SS Nemesis is very high quality one, the one that goes for 21.00 shipped. There quite a few upgrades you can get for them, extended firing pins, copper rice pin (connector part), and magnets switch upgrade.
Battery safety knowledge is given and should known first before even thinking about mech..if not..get fuse type device like Kick 2 or Siegeli Kick
GL, and happy vaping