300Blackout is great; the problem is availability and price of ammo. I had a 300BLK AR15 that I sold for $800 last year because ammo cost too much for me. It might be different if you reload though.
Venom, the Draco Pistol (Romanian) would be a good candidate for a SBR AK. They have chrome-lined barrels and good finish/quality for a basic AK. Your accuracy will be much better when you install a stock. Mine is harder to aim (for obvious reasons) so I put a red dot on it. The best thing is that it fits in a large backpack. One thing to note though is that it has the narrower magazine well which doesn't fit some polymer mags like Tapco's. Not a big deal since I always use steel mags and there is no magazine wobble.
Or you can buy both a AK rifle with a folding stock, and a AK pistol to save forego the SBR. Here is a comparison:
