I've owned three different versions of the semi-auto, and gunsmithed a number of them.
Accuracy with good ammo can be astounding, but is limited by the crude standard sights.
If you find and afford one, the fully adjustable Lyman-type original rear sight that has fine adjustments for windage and elevation will allow far better accuracy.
I've gotten and seen some really fine groups at 100 yards, and accurate shots can be made at even longer ranges.
The longer barrel helps, given that the gun is firing a .45 ACP cartridge.
Reliability with the drum or box magazines is mostly a function of the ammo used.
Cheap ammo tends to give problems, but there is some history of the early Kahr-made 50 round drums having some issues.
In off-hand shooting the drum will have at least a little interference with both the forward pistol grip and horizontal fore arm, but this is quite acceptable, especially considering what the Thompson gun was originally designed as.
The gun is an absolute HOOT to shoot, and always draws a crowd at the range.
This can be bad, due to the guns ability to just EAT ammo quickly, and everyone wants to shoot it.
The 1927-A1 Deluxe is the nicest and most impressive model, while the M1 versions would be most appropriate if you want a WWII look.