I cannot comment on the SU-16 but I have an early 580 series stainless Mini 14 with skinny barrel. The accuracy is not as bad as the mini haters say..2 moa at 100 yrds. Mine has the "pencil" barrel and its good enough for what I use it for which is hunting. Currently worked up a few reloads but waiting on better weather to test. Reliability?? After 200 rds, no fail to ejects or fire. I had one fail to feed due to the magazine. It was a Tapco mag. The mag follower would hesitate as it got near the top. Using OEM Ruger, unknown stainless and blued steel mags, I have had zero issues.
Cons, mags are more expensive(pricing has come down) and every one I had except OEM mags have needed fitting. The rear sights are hard to adjust due to not knowing adjustment increments and you will need a tool...but they do hold and work and are easy to use and fast. If you are putting it in a Sparta stock, then you wouldnt worry about this anyways. As far as accessories go, not much out there...again depends on your application. If going in a Sparta stock or the Troy MCS(discontinued), then you now have rails to add all the goodies to blow your whistle. Stock trigger is a little gritty and slight overtravel. A good trigger job("polishing" sear and hammer faces) will take up much slack and lighten the trigger somewhat. To stop overtravel, I drilled and tapped a screw right behind the trigger and adjusted it until there was absolutely no overtravel.
