"Regular" vs "LP" (low profile)
The "regular" models have a deep well around the 510 connection. It's there so that if you over squonk, the juice stays there unstead of running down the side. That said, as noted, you should only squonk enough to wet the wick, although the "extra" will be drawn back up into the atty over time. You can "blind squonk" by drawing on the atty WITHOUT firing, until you *just* hear a slight gurgle OR feel a slight change in pressure. That's enough to wet the wick and you're good for several nice vapes.
The "LP" models have the drip well ground down even with the 510 connector. That's so you can use wider atomizers like the "LP" RM2. The "normal" RM2 has had it's base milled just enough that it will fit into the drip well of a regular REO, the LP RM2 (not milled) won't fit into the well.
If you're going to be using disposable atomizers/cartomizers, you definitely want the "regular" version (to avoid drips). Many of us have switched over to the RM2, and in it's "regular" (milled) version, fits just fine on the "regular" REOs.
Some folks like to use a variety of rebuildable atomizers, hence the need and demand for the milled down (LP) REOs. You can use the "regular" (milled) RM2 on the LP REOs, it just looks funny because you can see the brass where it was milled.
It's all up to you and how you think you'll be using them, but truthfully, a year from now you'll have lots more REOs, so just take a best guess for now and don't stress over it too much.
Also, you can PM Robert (redeyedancer on ECF) to see if he can hook you up with a particular color combination you want in whichever one you decide to get. He's a great guy to work with, and doesn't mind at all if you call him up and chat about it, he obviously has insights few others of us have.
So, to summarize, the LP REOs can use ANY atomizer (pretty much), the regular REOs can only use disposable attys and cartos, and rebuildable attys that are around 14mm wide at the base or less. In it's "native" form, the RM2 wouldn't fit a regular REO, so Robert mills them down to fit.
Probably more info than you wanted, but it's always good to give as much information as possible, since there will be people coming along behind you, that know far less about this stuff than you do
(and just a little p.s., due to my own preference. You can slip a bottle cap o-ring over the brass part of the "regular" (milled) RM2 so there's no brass at all showing when you attach it to the regular REOs. Just a "looks" thing
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ETA: what they said above, before I could post all this
