I was thinking of binding it to my SF, since they both share the same CD; however, such a huge mana surge might lack in usefulness, at least early in fights, which would, make you delay the cast (or sort of force you into spending mana via expensive heals) in order to reduce/overcome mana being wasted. This in turn would reduce the amount of times you could use it during the fight. I usually cast my first MBender when I'm between 200k-230k mana which is usually a minute and a half into a fight (fights vary ofc). However ,with this setup, I'd probably have to delay it even further, to the 2 min mark maybe, which will affect posterior uses correspondingly. Mainly this will be a concern for shorter, and more mana-intensive fights, rather than longer, steady mana-usage fights (5-6 min v/s longer ones).
After all that blather, my question comes down to: Should I bind the trinket's on-use with SF, or just keep'em separated, even if that means another binding and CD to keep track of?