The RM 3,4,5 are new atties Rob has added to the site, they are not upgrades to the RM2. They are clones of different atties that Rob has drilled through the post to modify for bottom feed. Here is his thread where Rob talks about them and what they are clones of
http://www.e-cigarette-forum.com/forum/reos-mods/577376-atomizers-i-am-working.html
The RM2 Rob has done extensive work on, such as adding the ceramic base inside the atomizer. This is by far my favorite. The ceramic base means you can put your coil all the way down on the deck and it won't short out because, well, it's ceramic.
The newer atties pretty much came along because of the LP Reo. With the LP Reo, since it is milled down slightly it allows bigger atomizers to fit it, not that you have to use a bigger atomizer. Rob then modded some popular larger atomizers for bottom feed. I do wish he would call them by their name, or put it in the description of them because it has caused some confusion.
