How cheap 599?
Yes they are awesome, reviews on here and Buds have been magnanimous. The charging handle and handguard needs replaced but the barrels are voodoo melonited and the receivers are mil spec. Otherwise it's a standard milspec rifle with a same plane gas block and a high end piston system/bcg, for the price of a low end Smith. The gas block is pinned and very hard to remove(good thing, really).
For 599, they're hard to beat as a novelty gun. I wouldn't recommend it over DI for a first time buyer though. If it's your 3rd+ AR, go for it.
This thread will probably get moved over to the piston forums though. Other owners have some reviews over there. The Customer Service form AA is great, and it's a lifetime warranty on those guns.
ETA: If you can build a PSA CHF for the same prices, which is what I would recommend first. The gun is solid, but it's hard to get as solid as a PSA for that price. That said, the BCG on the AA is something to behold.