I have a RRA LAR-8, .308. Mine happens to have a lengthy barrel (26"), but one can make things shorter if one desires... just can't make it longer.
A nice thing about the LAR-8 lower - it uses standard AR parts. Meaning the trigger group for sure - I put a Geissele SSA-E trigger in mine, right out of a standard milspec AR lower.
If the magazine choice is an issue for you, the LAR-8 is designed specifically to take advantage of the millions of FAL magazines out there, and there truly are millions of them. I found them for $11 each, brand new. For a REALLY good quality magazine, Moses Machine Works, LLC is now producing an absolutely gorgeous magazine specifically for the LAR-8. I bought five of them and they'e as good as any magazine I've ever seen. Flawlessly functioning polymer magazines very much like other "name brand" mags.
The fit and finish of the LAR-8 is on par with any ARs I've seen and better than most. Since it is designed to use the FAL magazine, there are a couple of differences. The bolt release for one thing - it is ambidextrous and it's below the trigger guard just to the rear of the magazine well. I find it handier than a standard AR bolt release.
My 26" stainless match barrel is excellent to date. I have no criticisms of the rifle other than the fact that it's definitely not a lightweight. A shorter barrel will make it much more portable.
If I can answer any specific questions, let me know.