I see a lot of complaints about the two piece on multiple forums... And i'm having trouble believing that people actually need the SW Masochism for mana back. When i'm shadow in raids (Which is currently around half the fights) I never have any mana issues, and never have to SW unless moving before execute range. The only time i get masochism procs are because of unavoidable raid damage, or when i'm in execute range. The only possibilities i could possibly see for having issues with mana is if i'm forced to shield my self consistantly to help out my fellow healers, which is unnessisary on the large majority of fights, but even then you're taking so much damage that masochism should already be giving tons of mana back.
Just tested on a target dummy, and buff less i was able to do my full rotation for 10 million damage before running out of mana. With mana back from raid damage i can't imagine having to do more then that even on an extremely long encounter.