Unless you really want a 5.45 AR (corrosive), there is no reason to get a piston, and plenty of reasons not to, unless (possibly) you want to run a suppressed SBR/full auto with a decent round count on a regular basis. Otherwise, DI is: lighter, more accurate, standardized/cheaper parts, no carrier tilt, and lighter recoiling. Furthermore, if I had the dough to suppress and SBR stuff, I'd probably look into a SCAR for that role.
That being said; if I got a reeeeally good deal on one, I'd buy it, but I would say you can get a better gun for less money in DI. If you want it just 'cause you want it, then go for it.
