I'm somewhat surprised that this isn't (more) popular (at all). Other than this piece, the highest obtainable amount of subtle blow you can get is +5. I know there are plenty of people who can appreciate a mob they're trying to defeat solo using fewer TP moves.
I'll have to agree, dragonspight. Probably one of the most useful pieces of gear that goes by unnoticed. I love my PeisteBelt+1. You can get more subtle blow on a single piece though, if you're a thief. Dragon Harness +1 has 12 on it, and NQ has 10. Lord knows we thieves need it.