I reload several different lots of brass for several different ARs (and a few other calibers). The X-die works as advertised BUT, since I use it on different batches that came out of different chambers, I do need to frequently adjust it a little. That's a bit tedious; you're fairly likely to crunch a neck or 2 getting it set just right.
That said it's worth the price of admission.
IMNSHO, no need for a small base unless you're sizing milsurp brass that was fired from a machine gun ... I keep my brass batches separate per gun but it all started life as 1x LC and I've never had a need for a small base. Different story with some 308 I picked up - that was from an open bolt gun and demanded a small base.
/Bryan