To me, a carbine is supposed to have a 14.5" barrel. If I can't have that then I see no reason to half-ass it. May as well just get a full-length 20" rifle.
So I guess there will be no carbines or commandos in my future until they either repeal the NFA or I feel like paying the SBR tax.
If I was going to go with a $200 tax stamp, I would not waste it on a 14.5" upper..... I would go with a max 12" and probably a 10.5" upper.
Spending that kind of money and only cutting back 1.5" just seems silly to me...