IMHO, the Thompson is probably the easiest SMG to shoot accurately, mainly because of its weight. With the comp, it is pretty easy to keep a 50 round drum in a pieplate at 10 yards.
The bolt mass moving forward can be noticed, but not like the M3 or the STEN. There are pictures of shooters leaning into the gun or adopting some exaggerated positions, but I never found that necessary, nor did I ever step on the sling, as some have recommended. With the drum, I think the gun weighs about 17 pounds, and it is not going anywhere shooting a pistol cartridge.
Jim