I have a MPX pistol that I did a Form 1 SBR and it is definitely one of my favorite guns. The only disadvantage compared to other 9mm carbines is that unlike most that use Glock mags it has a proprietary magazine made by Lancer. They are excellent mags but stupid expensive.
You can build a 9mm carbine. I have done three. I prefer the New Frontiers Armory side charging design. They are Glock comparable. I also build this as an NFA SBR.
If you are building, you have to tune them to cycle properly, between BCG mass and buffer spring. But once running, they are great, and yes, you get a pistol and carbine in same caliber with compatible mags.