I have been using the Fluval 404 canister for about 2 years now and I love mine also.
It holds tons of media and it is a breeze to clean.
I have never had a problem priming mine.
I just hook it back up after cleaning and pump the little prime handel a few times and away it goes.
No problems with air bubbles either.
It's also a very quiet filter.
I agree, mine works great, another friend at work has a smaller Fluval and it works great also. Neither of us has trouble with air bubbles and it is probably the quietest filter I own. The only reason I have trouble with priming is that the intake strainer has a small ball that goes up and down when you prime the canister. My intake strainer broke off and the ball has been lost, I easily put the strainer back on, but have no idea where the ball is! to I plan to buy another Fluval 404 in the very near future.