Well. An sbr in either length would be a fun "toy'' range gun.
They both could be good house or vehicle guns as well. I don't know, besides looks, if the super short barrel would have much of detriment on velocity to affect bullet performance. 7.62x39 isn't nearly as dependent of velocity to do it's job like the 5.56x45 round.
Either length would be cool to me. But personally I like the look of the 12 inch model better. The 7 inch one looks a little to "stubby" or "stunted" to me.
And the 12 inch one would be plenty short for "serious house work".

Comparing the 12 inch one to a standard M4, the 58 carbine (not the compact 7.5) would be nearly the same length as a retracted stocked M4. Obviously smaller compared to any M4 with the stock extended to any length.