Are you sure he wasn't talking about the Reising submachine gun?
The Marines had a lot of second-rate equipment early on in WW2. The guy who decided Marines were rifleman and needed to keep the 1903 didn't figure on the massive shortage of 1000 yard targets on Guadalcanal.
Everything I ever heard from WW2 veterans in the family (father, many uncles, a few cousins) was that the Reising was hated by the troops, hopelessly unreliable and inaccurate, likely to be "lost in combat" at any opportunity.
Still a bunch of M3 and M3A1 SMGs in Vietnam during my time there. As others have noted, very slow cyclic rate of fire. Combined with the weight of the weapon and a 30-round mag of .45ACP I found it easy to control, even able to squeeze off individual shots, recoil in full-auto was not difficult to handle and maintain reasonable accuracy (at least at handgun range, which is about the limit for this type weapon). The collapsible wire stock also served as a take-down tool and magazine loader. Sights were nothing more than a folded sheet metal aperture rear and blade/post front, fixed and non-adjustable.
The M3A1 featured a cocking lever, easy to used and an improvement over the original M3 with a simple finger hole in the bolt, but also a bit awkward since it protruded from the side of the weapon (as did the folding bolt cover when opened for use). Very simple operation and easy to maintain, not finicky about lube or fouling/dirt/dust/water.
Interesting accessory item was a short piece of pipe with a 90-degree bend and a wing-nut for mounting at the muzzle, allowing the user to shoot around corners without exposing himself. I think this originally was a means for tank crews to protect against close assault by sticking the weapon out a port or hatch and firing.
Overall, very utilitarian, easy and fast to produce, and very inexpensive to make.
