Got this at R44 and I am suitably impressed with it. Here are the two spells so you can compare:
Siphon MP II
I was getting anywhere between 145-195 mp back on a single cast on a single mob if unresisted. Multiple mobs was netting me 500+ so this spell has got a lot of power for me as my THM's MP pool is hovering at just over 1k. All this for 15mp more.
Another spell you can look forward to I would say and another one CON's will rank THM up for.