Mechs are great in that they are simplistic and have no electronics to fail. But they are dangerous if you don't know what you are doing. With that RDA I'm guessing you want clouds and low resistance builds. You can actually get bigger clouds out of a regulated mod. If you are set on a mech, they are all pretty similar in how they work. You will see lots of folks argue about voltage drop, sleeve resistance, etc. In the end, mech are about looks. Find one you like, put GOOD BATTERIES in it, and don't build below 0.5 ohms until you know what you are doing. Make sure you have an ohm meter, TRUE 20A batteries (LG HB6 or Sony VTC4) and don't try to go crazy with your builds until you have some experience. And above all else, stay away from hybrids like the SIMPL.