Flatline, let's see, I have a decent chunk of experience in it. Enough to never want one for myself (I sell them all the time on tippmanns to local buyers)
1) accuracy=poor. Not horrendous, but poor. I believe the real reason for this is the backspin. In a perfect world each ball would come out rotating on the same exact axis but we don't live in that world. So each ball comes out spinning on a slightly different axis and that very slight side spin pulls the balls left or right over their flight
2) Extra range = none. Will the ball go further? Yes, will it break? No. Not unless you get some super lucky shot onto the spike of a Gothic spyder.
3) flat trajectory = yes. This one works as advertised. Some players like to say it's a better trajectory but really it's just different. You can avoid low hanging trees and shoot though multiple windows but you lose the ability to drop balls in over walls or into sunken bunkers
4) paint options = limited. In theory you want some brittle paint so that at the "extended range" you can still get breaks, the problem is getting that brittle paint to survive the curve of the barrel is difficult. Realistically, think of having a stock a5. It's rough on paint, you need something with a slightly thicker shell
I always tell players get a apex over flatline, it's adjustable backspin, you can turn that into a side spin or even down spin but the best feature I think the Apex has is that you can turn it off