My go-to rifle is a Kel-Tec Sub2k, because it's compact and easy to travel with, and I presently qualify as a poor college student. It is also the first gun I've ever had that isn't 2-3 times my age. My fondness for it brings me to consider the place of subguns in the modern world.
Despite being a good deal smaller and lighter than most intermediate caliber carbines, it lacks any of the penetrating power or end effect while possessing only marginally lower recoil. AP rounds exist in 9mm, but are banned from sale to civilians. Likewise, the long barrel improves the power of the ammunition, but this in turn puts the ammunition outside of its intended ranges, causing weird, sub-optimal behavior, at least at close ranges before the bullet slows back to usual speed.
No matter how I look at it, no matter how much I love the handling and feel of pistol carbines, there's really no two ways about it; other than sharing ammo and magazines with a sidearm (maybe), they combine many of the downsides of a rifle with the weaknesses of a pistol.
At least they're (usually) inexpensive...