JT two piece, tear drop (Testing the hammerhead barrel over the next year)
Black Dust Angel Speed, Cradle with On/Off, CP locking feedneck, SS Freak Kit with AA Tip, Killer Gripz sightrail/pull knob/snatch grip/back plate, A4 board, 91/45 bulldog tank, Smoke Halo B
Any except really cheap, only had problems with Zap rec series paintballs.
Stainless steel, amazing accuracy (best I've tried so far), great selection of bore sizes.
Price, extra weight if using the stainless steel back.
I've experienced some amazing feats of accuracy with this system in tournament play managing to hit players with a small burst (the entire string of balls hit) from almost clear across the field with only the top part of their hopper showing. I was amazed at this and also got a warning from a ref for overshooting. Though I think it must have been obvious it wasn't on purpose considering the how far away I was. Interestingly enough the opponent I eliminated wasn't impressed by the accuracy of my shots.
Considering the problems I've heard other people have with smart parts barrels in general I can only say I either have the only well made production model they have ever made or only those people with problems mention anything about this system. I can easily shoot through a barrel break (I have three different threaded backs for my kit) and have only broke a ball twice in this barrel on my Angel but my sensi was shut off both times as well and the paint wasn't all that great.
I'm sure this isn't the greatest system out there, they all have their strengths and weaknesses and I'm not sure if you really need the stainless steel back unless you put your marker through hell on the field! This barrel system as great as it is won't stop me from trying others to compare them.
All in all I am impressed with this system and would recommend it without any problems with one exception. I would suggest the AA tip not the Freak tip unless they have fixed the problems I have experienced with it. Specifically the Tear Drop porting tore up my squeege and rips off parts of my swab making it hard to clean.