Well, the function of the springs is mainly what Mark said: to help pad return. For bleeding, zip-ties/old pads avoid the piston from pulling out (pretty much like a disc brake).
They are some pretty big holes indeed (thought it was a bit of a failure when first got the brakes); but on the other hand you get 2/3mm to play with. By the way, this never caused the slave/clamp unit to move, and I noticed the bolts needed to be tightened much less than on Magura mounts (any HS33 mounts I mean, tried ZHI's, Maguras, Try All's).
Also, I ve been using the brake for 2 and a half months now, no leaking, everything in place. It's just another option: the brake works as good as a well-setup Hs33 could; I say if you want a much easier setup, try this.