On the pro 4 it was never that hard to get those rings off, mine are usually mangled on the cyclone.
If you are really lucky you can pull the wheels and hex hubs off and slide out the uni and at the right angle i think you can get then take the uni out without taking the ring off. But thats quite a pain to do as well.
From a performance perspective the aluminium outdrives should be better but the blades are expensive. Just make sure you change the blades aka. the plastic C thingys aka. i think HB refer to them as diff adapters (or reverse them) before they wear out. Once you get wear on the aluminium outdrives the blades wear out faster (and unfortunately they are not cheap and sometimes very hard to get).
XRay blades will apparently fit as well if you are looking for something.