Hi:
At the beginning of WWII the drum magazine and vertical hand grip were common. As the war progessed the stick magazine and horizonal hand grip became more in use.
The British preferred the drum magazine and vertical hand grip.
The Model 1928A1 was the Thompsons in inventory with stick magazine and horizonal hand grip when I was in the Military along with M1A1s and M3 Grease Guns.
Jimmy