I have had a 306 running for about a year now. I've started to cycle some of the bio media out, about 6-10 pieces a month in one of the tray's since they are slowly breaking down. Have 2 Blood parrots, and a Tiger Oscar in the tank, the BP's are lower quality, now adult, but not as large as most bp's, the Oscar is about 3-4 years old now about 9-10" long. I purchased a spare impeller, and gasket. Thus far no need to replace anything. When I do a deep clean I rinse the filters, and gently jostle the bio trays in tank water, about once every 6 months, or as I notice the flow slowing down.
I use the filters the unit shipped with, saw they sell replacements at PetCo the other day when i was there looking around with the wife.