I've had a Oase Biomaster 600 on my heavily-planted Aquael 240 since early November. Like many others here, I've had issues with it purging air. It's done so much more than any Eheim, Tetratec or Fluval canister filter that I've had.
About a month ago, this purging stopped. It co-incided with me doing something I'd foolishly neglected; I put my hand in the tank, and cleared away the debris clinging to the filter intake tube. Immediately, the flow increased, much to my embarrassment, given how long I've been fishkeeping! As I say, the other effect was to more-or-less eliminate the air purging.
Now, I know what many might say at this point; correlation isn't causation. It might simply be a co-incidence. It might simply be that, after all these months, the filter has bedded in.
We'll see. The Oase does suffer from complication, insofar as it has so many sealing rings that can go wrong, and let in air or let out water. On the other hand, it's the most impressive canister filter I've ever had. Its prefilter system is a thing of wonder.