If you are considering buying a mech then there are some things you need to know...
First of all, battery safety and ohms law are required knowledge. Let me be more specific, knowing about battery safety and ohms law isnt enough, you need to fully understand both subjects before using a mech. The following blogs should help you get started:
Mooch's blog | E-Cigarette Forum
Baditude's blog | E-Cigarette Forum
Next thing I would say is that I simply dont trust direct to battery mechs(or faux hybrids as they were once called, and still are in many cases). They require the use of atomizers with a protruding pin in the 510 connection and can be highly dangerous if the pin isnt long enough. Thats not to say they cant be used safely, but I just dont trust them. I prefer mechs that have an adjustable pin in the 510.
I would also mention that I dont trust the use of a prefab coil on a mech. For mech use, I would say that building your own coils and the ability to monitor your build is crucial as it allows you to keep an eye on things and make sure nothing is shorting out on you. I know of some people who use prefab coils on mechs and have success but its not something I would recommend. I dont even like the idea of using an RTA on a mech. I strongly believe that for mech use RDAs are the best option available.
With a solid understanding of how mechs work, battery safety and ohms law, they can provide an excellent vape. They can provide massive amounts of both flavor and cloud but it is 100% dependent on you and your understanding of how to build effectively and safely for your desired result.