Yeah I don't think the STR is so much better than a SOPMOD to actually replace a SOPMOD if you already have one, which is why I still have 2 SOPMODs on lowers (SR-15 and dedicated .22LR lower). :) but for any future lowers, an STR is definitely the way to go for me... and if people still paid LMT prices for LMT SOPMODs, I'd sell one and buy two more STRs! Damn you B5!!
I don't think a UBR is even worth it on a suppressed SBR, my 10.5" 5.56 SBR with AAC SDN-6 (20 something oz, 7.5" long can) balances at the muzzle side of the magwell. Removing the can moves the center of balance back even further, something like mid-magwell. That's one of the advantages of a short barrel, less center of balance shift with a can! My SR-15 center of balance shifts FAR forward when putting the SDN-6 on it, so much so that I'd prefer running it with a battlecomp than a suppressor unless I could cut it to 14.5" and run a Mini4 or something similar... so maybe a UBR would work on my SR-15!
But I never understood why people got a UBR just for extra weight. Yeah it looks neat and saves you from buying a buffer tube, but you could just get a STR and fill the battery tubes with lead weights for the same effect at less price.

