You're gonna PI every odd MB and at least with my normal haste levels (1071 rating) I get 12% back and 15% mana back with PI which is a bit more than Solace.
5 stack AA with solace:
3 solace (0 mana) + 1 offensive penance (2.3k)
5 stack AA with MB:
3x penance (6.9k) + one freed up global which is probably a pws for 3.8k.
So really you're spending 8.4k mana more every 30sec which in 2 min will be 33.6k = 21% of mana. Mindbender GCD Edit: 33.6-3.8=29.8 which is 18.6% of mana.
So that minus the difference in mana reg from solace vs. MB (3% every 2min) = 15.6% less mana from MB than Solace every 2min. That's worth 504 spirit. So the question then becomes whether you wanna drop 504 spirit from jewelry for secondaries or the extra pws every 30sec which will be about a 1875 hps increase (given it averages roughly 75k).