OK, either I build an AR-15 for $700 or buy an SU-16 for $550.  The extra $150 could buy a lot of accessories for the SU-16, but I'm worried about long-term performance of a mostly-plastic gun.  Has anyone found the plastics on the Kel-Tec wanting for more strength and durability?

This weapon is still pretty new, so time will tell how durable they really are. Plastics have come along way and if made properly, they will be extremely durable. I have had some experience with these guns and I would suspect they would hold up just fine.....but the SL8 suffered from cracks, so we will have to wait and see. Build an AR, no doubt about durability there....will outlast you.
I would also reccomend the "new" Mini 14 which is superior to the SU-16 and is about the same price. The SU is a cool gun, but I wouldn't ever buy one.....for the money, you can do better.

IMHO your price estimate on building a decent ar is kinda high.Well,I was going to post a link to an A2 kit from J&T for $450,however their website is under contruction.Here is a stripped lower from rbprecision for $90 plus shipping.You can build a good ar for about the same money as the keltec rifle.The su-16 does look sweet though,especially for a compact trunk gun.As for the durability,only time will tell.I would like to pick one up someday though.I have to say,havnt heard much bad about them,most that have them love them.
As for the mini,with the AWB going away and the ability to put a folding stock on it,wouldnt be a bad choice.Decent highcaps are easier to come by now,and there are quite a few easy mods to help with accuracy.Good Luck.

i had a keltec p11 for a few years. it was a good reliable little pistol. one day i pulled the trigger and it snapped in half. there was no more trigger hanging out of the frame. i sent it back to keltec and the stamped a new pistol with the old serial number for free even though i was not the original owner like the warranty covers. i lost all faith in keltec as a defensive weapon. i sold it and the p32 i had. get the ar or better yet an ak.

Quoted: IMHO your price estimate on building a decent ar is kinda high.Well,I was going to post a link to an A2 kit from J&T for $450,however their website is under contruction.Here is a stripped lower from rbprecision for $90 plus shipping.You can build a good ar for about the same money as the keltec rifle.The su-16 does look sweet though,especially for a compact trunk gun.As for the durability,only time will tell.I would like to pick one up someday though.I have to say,havnt heard much bad about them,most that have them love them. As for the mini,with the AWB going away and the ability to put a folding stock on it,wouldnt be a bad choice.Decent highcaps are easier to come by now,and there are quite a few easy mods to help with accuracy.Good Luck.

+1 on the Kit from J&T or Model 1 Sales.  For $450ish you can get all of the parts you need.  Another $90-$100 will get you a stripped receiver.  May not be the best AR in the world but for the money it beats out the SU-16 any day.  I'd take a Mini-14 over a SU-16.  Might not be very accurate but at least its been proven in the law enforcement circles throughout the US.

Here is a review done by one of our members in Kali over in the survival forum on the SU-16.

Personally I'd get a Saiga .223 with 10rd mag for $200 before getting a SU-16.

.....but the SL8 suffered from cracks, so we will have to wait and see.

I got two SL8's and would like to know where they crack so I could check them out.