Barrel - pretty accurate for a stock barrel. SP usually puts out good barrels, but honestly this marker can much quieter and accurate with a barrel upgrade, ie CP barrels, Freak barrels, All American barrels, even a Evil Pipe Kit. (REMEMBER: ION takes IMPULSE threads.)
Feedneck - I think its pretty high. Gotta get a low profile feedneck. I don't really have a suggestion on which on cos' I still have mine stock, but I'm planning to buy maybe the q-lock, or any other low rise feedneck. <~ personal preference.
Reg - I wouldn't spend your money on this upgrade, unless you have a personal preference. I like the reg. You just need to break the sucker in, that's it.
Body - I like it. ITS NOT "plastic", its "polymer." Same thing. However its polymer coated ALUMINUM, Therefore DURABLE! You can sticker the snot out of this gun. Totally pimp the body out. I personally might get carbon fiber stickers and sticker the body, well portions.
Internals - Big FAN of SP internals. High Quality, I think. But one thing I didn't like is disassembly. It was pretty tough, but honestly this will make you a better tech if you can disassembly this sucker. Also, the hoses are exposed, but so are the timmy solenoid hoses. Oh well.
Board - People. Listen. 17 bps is pretty fast. Not gonna lie, I like no cap, but this is a very good board with a very good eye system. Vision eyes, I think, are the best out there. Besides...a month or two...there will be a board and I'm going to get one. You can get one right now at zdspb.com, but still won't go faster than 17 bps because of....
The Bolt and Solenoid - watch out for these aftermarket upgrades. THIS WILL MAKE THIS MARKER GO PAST 17 bps. SP said they have reached the low 20s with the ION, but I call BS on that. However, with these upgrades plus a new board (Please WAS make one!) you'll get your fast marker.
Feel - is great. So freakin' light!
Duckbill ASA - I HATE IT! makes the gun way to long. I just don't like the fact that SP says its better to get an Off/On for the marker. why not put one on? oh well. Get a NDz, CiP, or custom products RAIL-Off/On COMBO
Trigger - its not bad, but not good. It helps to take off the magnet to make it less stiff and also you can go to pbnation.com forums and a dude is making custom triggers that are pretty phat. I'm getting one...
Noise - I like it. Not noisy at all, really. Like I said, getting a new barrel would probably help with reduction of noise.
Durability - OH yea. One thing. There is a review out there by Sporefrog which says that this ION is horrible BLAH BLAH BLAH and is not durable. He states that he "slided" into a bunker and hit is hopper/feedneck on the ground. Well, if you slided correctly you wouldn't have this problem NEWB! anyway, just venting. This gun feels durable, and has the ability to withstand tournament style play.
Tank - It would be helpful to get a HP tank. You can get a LP tank, but make sure you get a Crossfire because they have the best recharge for their LP tanks and ONLY use them if you have a LP tank. I know people use other LP tank, but that means more tinkering with dwell and reg press BLAH BLAH BLAH. Also, you could get shootdown. Honestly, this gun's pressure is perfect out of box so do yourself a favor, invest in a HP tank. I am. 