The only difference is the casing Eheim have made the new one more user friendly.
By using a clip the item has no chance of popping apart the old Aquaball was a bit prone to that.
IMO the new Biopowers are better, you can either have the sponge inserts, bio media or mech media, like bob sais, they are better designed, also are grey so hide in the tank better!
I've not got a Biopower (I have the 2nd generation Aquaball) but have had a good fumble with one. The main difference is the incorporation of 'external filter technology' :dk:
What they mean by this is that instead of having the media baskets with fully open cages, allowing water to enter all over the media along the length of the filter. They had closed all but one of baskets, the bottom one. So that there is only one basket with an open cage, so that water flows through this one and upwards through the media in the closed baskets.