I have some 14" Contender barrels. In my younger days I could shoot them off hand, even one handed tolerably well, but they simply were not made with that in mind. Even if the weight isn't too much for you, the balance is simply "OFF" with that much barrel. They are made to be fired from some kind of rest.
The same gun with a 10" barrel still does its best work from a rested position, but it is a lot easier to use offhand than the bigger, heavier longer version.
The .300 Blackout has no use in my shooting world, I'm not very interested in ARs, and I don't run suppressors, so I don't see the point of it in a single shot pistol, unless you are already using the round in other guns.
There is nothing the .300 Blackout does better than many other common rounds, other than run in suppressed ARs, if that's your thing, enjoy!