I love to see the bold choices ok butterfly's in reefs with sps. I have one tank myself dedicated to it.
Yes, I am definitely not afraid to put "reef safe with caution" fish in my SPS tank. 95% of my zoas did not survive my angel/butterfly additions, and all of my pectinias and war corals do not have eyes anymore, but the losses are definitely worth it!
I believe the key is that my sps colonies were already established when I added the angels and butterflies so all the nipping (and I do see a constant nipping behavior) is tolerated. New sps frags, on the other hand, have a tougher time surviving - but I have not cared to add any new corals in my tank for some time now. If anything, I want to thin out some of the variety to allow the larger colonies more room to spread out and grow.
Back to the bellus angels - I am seeing them more and more in the aquarium trade in the last year. Three years ago, they were difficult for me to find - and when I did see them, they were large adults. Now, the perfect 1-2" size specimens are everywhere and they are coming in looking very healthy.
I have contemplated picking up a couple more of them to get a large group of them, but since they don't seem to group together in my tank anyway, getting more of them would not provide much of an impressive display.
A couple of other positive tidbits about them that I love:
1) They readily take pellets
2) They tolerate treatments well - All three of mine continued to eat through prazipro treatments
3) They show no aggression towards other fish, even smaller, docile angels
4) They're the only predominantly reef safe blue fish that I could think of that isn't either a tang or a damsel!