If you have to use them, firearms with stocks are better than firearms without stocks. Two of the best reasons for this are accuracy and speed. Another reason is power, but the last is not true of Pistol Caliber Carbines. PCCs don't have much power advantage over handguns in the same caliber, but they are still more accurate and faster in use than handguns. PCCs can also reduce ammunition supply challenges, since shooters can use the same ammunition for their sidearms. When using a magazine-fed automatic pistol, some PCCs can be loaded using the same magazines.
A few handguns in the past have been convertible to carbines, usually by means of attaching a stock to the back of the handgun. The Mauser 96 is one of the best-known in this category.
Glock handguns have taken over the lion's share of law enforcement sales in the United States since establishment of an office in Georgia in 1985. Glock handguns were sturdy, lightweight, simple to maintain, had a very high ammunition capacity, and reasonably priced. As law enforcement bought the new handguns, citizens did, as well. Some consumers, impressed with the sturdy and simple Glock, wanted a carbine with the same advantages. Despite occasional rumors, no Glock carbine has been forthcoming, though firearms company Kel-Tec has offered their Sub-2000 folding carbine in versions that take Glock magazines. Company Mech-Tech has been offering a conversion from handgun to carbine for a while, but their version looks rather jury-rigged. But a new product is on the scene.
Hera Arms has built what is apparently a "drop in" Carbine Conversion unit for Glock 9x19mm, .40, and .357 Sig full and compact models.
It would appear that this was at least suggested by the Magpul FMG-9 prototype. The FMG-9 looks more elegant, but definitely more complicated. And, so far, it's vaporware.
The Hera GCC definitely has all kinds of eye appeal over the Mec-Tech, but U.S. owners also face the frivolous restrictions regarding Short Barreled Rifles. Rifles meant to be fired from the shoulder must be at least 26" long, and have a barrel at least 16" long. The GCC does not meet these standards, since the base model apparently just uses the barrel already in the Glock in question.
So: looks cool, but be prepared to pay another $200, on top of the $500 base price, plus the price of a Glock if you don't already own one. As long as you live in a state that allows ownership of SBRs.