I have the folding stock/M3 mag conversion kit, and I really like it. Including the kits, a couple of hundred dollars more than a semi-only Thompson. When I got my mags, they were $10. apiece (compared to $45. for the HK 10-rounders).
EOTech M552 holosight on mine, which is NOT in line with the iron (plastic?) sights, and pretty high above the barrel.
Accuracy- just like all my guns, more accurate than I am capable of right now. Essentially has a free-float barrel, but the receiver is polymer so you can flex it if you wanted to, although you wouldn't be able to while you were shooting it.
Reliability- I only put a few hundred rounds through it before the conversion kit went on it 2 years ago, and upgraded the conversion to a folding stock this past year after the AWB sunset. With the M3 mags, never had any problems, but I miss the bolt-open after last shot feature.
It also seems to attract a lot of stares at the range. Everyone who has shot it liked it.