does anyone have any unique insight to this?
I have some, but I don't think they should be considered unique.
First one is, that since May 19, 1986, no private citizen in the US has been allowed to own any full auto firearm that was not on the ATF's civilian registry list at that time.
SO, NO Glock 18, even if you can and do have other legal machineguns, because the Glock 18 (select fire gun) had not been created before the effective date of the law, and so there are none legal for private citizens to own.
Police agencies, and machine gun dealers may own them, individual private citizens cannot.
Next point, when comparing pistol size semi auto versions of SMG against handguns designed from the ground up as handguns, for just about every useful, practical thing, the "semiSMG" pistols, suck.
For cool looks, for acting out Walter Mitty type dreams, and for being the closest looking thing to an SMG that ordinary folks can still own. they're great. For accuracy, (being able to shoot them well), for weight and balance, and ergonomics they lose out to regular handgun designs.
I've had a Cobray (Mac clone) and a Tech 9 and also a semi auto Tommygun, so I have some experience with both basic styles, the "T" type (mac uzi, etc) with the magazine in the grip and the "classic SMG" style with the magazine forward and the pistol grip at the rear.
They are great guns for spray and pray, fun blasting plinking, and very impressive to people in general, but for serious shooting, PRECISE shooting, they are miserable compared to a regular pistol.
The "T" types are the worst to try and use as handguns. As carbines, with a shoulder stock they are a very different thing, but as handguns, they are miserable.
The sights usually are crap for easy, accurate shot placement. Some of them have fixed peep sights, and a small hole in a vertical plate at the back of the gun simply sucks to try and use holding the gun at arms length as a handgun.
The balance is really poor for one hand shooting. And even though they are bigger and heavier than usual pistols, FELT recoil is worse, due to their designs. The Uzi/Mac style guns with a 90 degree straight up and down pistol grip in the middle of the gun with a heavy bolt moving back and forth on top of it makes the gun "flip" or "bounce" front to rear, Up AND Down over the pivot of your grip as you shoot.
Trigger pulls generally range from poor to miserable. The Mac/Cobray style guns often have the safety located a couple inches infront of the trigger guard. It cannot be operated by the shooting hand when holding the gun in a firing grip. The safety on a Tech 9 is the bolt operating handle (push in for safe) and also cannot be worked by the hand holding the grip.
The Uzi has the safety in a convenient place (right above the grip) but suffers from the other drawbacks of the T type designs.
For any use where my life and safety are at risk, I'll choose a regular pistol over the SMG style, thank you.
For fun, the SMG types are great fun. But they aren't good choices for self defense and being only semi auto, they are inferior to their select fire "cousins" for military combat.
Simply put very, very few people can use them as well as they can use a conventional pistol.
Hope this helps...