The gun is light, and foldable and i'm being nice by saying that's its only strong points.
It's not accurate, unless you count 4 moa on a dead silent day accurate. With decent ammo. The trigger is pretty bad, but there is a trigger and spring kit you can buy to fix that.
The sights are quite terrible. You adjust the rear sight by unscrewing it and trying to adjust it by hand to where you think it should be.. then tighten it up (The sight moves as you tighten it..). So red dot is almost mandatory in my opinion.
The bi pod is really bad. Even on a wooden shooting bench it isn't very stable. A $20 UTG bipod on any rifle is better quality than the fold down bipod on the SU16F.
A lot of them have failure to feed issues with LAR and various mags. You can get a gunsmith to adjust your feed ramp - but they hate working on them because there is no room to work on it, and there isn't much material to work with (versus any other 223 semi auto rifle out there). Also, because the two included mags mostly still work with the rifle, it isn't a warranty issue - they won't help you.
As for quality, well, there isn't much. I shot standard 55gr 223 and hope it doesn't fall apart (screws can walk out) or the receiver can crack. I would not use 5.56 at all due to the various problems with the receiver cracking. Examples are found easily online. I'm not certain if this still affects the newer generation of kel tec rifles or not.
If you want a warranty, you have to buy it new from an authorized Canadian dealer. There is no warranty for used purchases for kel tec. You need an original receipt showing serial number in your name for warranty work.
I'm sure there are lots of folks who have run thousands of rounds through their SU16 without issue, and have a more accurate rifle than I had. Key word here: had.
If you bought one new from a retailer, at least you could hold some water with Kel Tec if you had issues with the rifle as they have a lifetime warranty.