Damn, i was going to say the same. Possession really solved most of the problems i had. Never leave home without it.^^

it's not as good overall, but it is totally idiot proof.

I would say until you get the correct metatechnique, it is quite the other way round. It makes YOU hard to kill and can give you an advantage by overtaking enemies, but you still have to bind spirits to get the full use of that, if the possession fails you really get a problem AND you still get a problem by controlling the spirit not to do stupid things. I think it is so difficult to handle, that it is a higher step of roleplaying compared to a standard-mage with materialization.

If you make something idiot proof, the universe will make a better idiot ^^

Meh, most "posession" Mages that I've seen or read about tends to fail the entire "roleplaying" tidbit you mentioned so at best I'd say that there isn't a difference between the two types when it comes to roleplaying.