IME, the gph rating SunSun gives is probably the bare pump sitting in water. Once you take into account the hose and fitting restrictions, and filling it with media, you will probably lose at least a third of that flow, if not closer to half. I would say you’d be lucky to get 800 gph once it’s all setup. That’s still really good flow though.
Unfortunately, I don’t have any need for one of these filters and will probably not be getting one, at least not anytime soon. I do have a 303B on my son’s 29 gal tank. My 220 has a 55 gal sump though, so I have nothing to put it on.
I am looking forward to hearing from anyone else that gets it for one of their tanks. If I had to choose between this or an FX6, I would go with this HW-5000 for sure.