I have a carbine barrel, a 10" pistol barrel, and a 16" upper for my AR in 300Whisper. It really is a great cartridge. Recoil is VERY mild. All three barrels a very accurate. I load 18.3gr of H110 behind a 130gr Hornady Single Shot Pistol bullet. If you don't want to reload, factory ammo is available from Cor-Bon in 125gr and 150gr. I also have some 110gr bullets loaded for "non-deer" use. I will readily admit, though, that I have no experience with the 7mm TCU. I would probably like it as well.
Go ahead and get the 300, if you don't like it for some reason, you should have no problems selling it on this site.