vaptamist and I have found that there are a couple specialized rebuildable atomizers (the Odysseus, Mark-T Infinity, possibly others) that have some problems making contact on a P+16340. Anything standard (510, 306, i06) present no problems with it. The SmokTek flanged cartomizers in a tank probably also might not work.
I'll have to leave the commentary regarding P+ vs. Ego for somebody more experienced with an Ego.