Agree with the answers above but a few points I'd like to add: first, mechs are great for sub-ohming, which while not the only reason to get one, is a good one (just remember to use the safest batteries - VTC5s are a good way to go). Also, there's something aesthetically pleasing about a nice mech. While you can sub-ohm with certain regulated devices such as DNA30 mods (down to about .5ohm or so), they aren't really designed for that (except for a device like the Axis or the GI2....). If you're going to go the mech route, just remember to be safe. I'd start out by buying a clone for a local B&M and have them build a coil for you. Personally, I'm a fan of drippers and that's all I really use today. Everyone has their personal preference and mechs are great for customizability (is that a word?). Like others said above, you will get a voltage drop so just be sure to keep a set of fresh batteries charged and you'll be good to go. Remember, the lower you go on resistance, the quicker your battery will die out.
If you're pensive bout coil building, see if you can have your local shop demonstrate it for you or watch youtube videos. There are a bunch that are quite helpful. Also, if you're just going to slap a carto tank or a clearomizer on top, I wouldn't even bother. However, if you're willing to plunk down a bit more change on a kayfun or taifun/fogger or RDA, then it's a solid avenue to explore.