Are these identical to the MKII Ruger?
Use Ruger MKII mags?
Talk to me about any issues, functional problems.
Any other thoughts?

I have 2, one with a 5" barrel and one with an 8".  The 5" is on a Ruger MKII lower and the 8" is on a MKI lower.  My AMT mags fit as do the Ruger.  The only differences are the AMT barrel is groved for scope rings unlike the Ruger where you have to buy those ugly scope mounts.  Disassembly/assembly is the same pain in the ass as a Ruger.  When I need parts, extractor, sights etc I just order Ruger parts and they fit just as well.  I've had mine since the middle 80's and haven't had any problems.

The Lightening was based on the Mark I not the Mark II.  Although like the Mark I upper they can "sometimes" work reliably on an Mark II receiver.  The Mark I Ruger magazine is the correct magazine, again the Mark II can "sometimes" work reliably, but you'll have better luck with Lightening and Mark I magazines.

These were pretty well made, and being made of stainless had a certain appeal.  But, there were legal issues and AMT stopped making them.  Of course, Ruger came out with the stainless Mark II, so that dealt with that issue.

I have always like the barrel profile of the Lightening.  Not necessarily more than the Ruger, but it is attractive.

Quality wise, some of the early Lightenings had reliability issues, but later production seemed to have ironed them out.

Unless it is super cheap I would just get the Ruger.  I have seen several with the extractor slot in the barrel over cut.  Requring the barrel to be set back and recut.  Lots of money

I went ahead and got the gun last Saturday. Took it to the range Wednesday.
Put 200 rds of Fed bulk pack through 3 MKII mags and 1 AMT mag.
Ran real good and I had 1 FT EXTRACT in the middle of the session.
Overall, I'm  happy with it so far.