I finally got around to try it out, but my god.
He does get pretty huge in collossusform, but damn, friggin long recharging time. I thought you were excagerating when ya said you could get a cup a coffee and be back in time, but it's true, it takes like 5 minutes to recharge.
But the upside is, the added damage is pretty nice, doing MF runs on Minotaur and 1st Telkine for a while and also levelling at the same time, and found some nice stuff already, but as soon as I hit lvl 22 I'm going on to the next chapter.
