the problem most run into with the Remora is they are not efficiently surface skimming so they do not get optimum performance. In tank a self adjusting surface skimmer will help a lot. The one AquaC sells are not very good you need on like Hagen makes that are self adjusting to water level. The other issue is there is no air control. Other issues can be the venturi getting clogged the smallest piece of anything will kill production. They do a decent job and may take a week or so to start producing depending on the bioload of the tank.
The issue with running the Remora skimmer on sump is the drop of the water. When I ran mine in sump I just used a piece of acrylic at a an angle for the water to run down to stop noise and salt spray. My pump was place where the over drained it worked well.
Over all for a HOB skimmer it works well but once you are running it is a sump, well there are so many better option. I have run AquaC skimmers for over 8years and still do, I like their EV series they are built like a tank and do their job well. But when the Remora and Urchin came out they were in a different time well before skimmers got smaller and more efficient. They were at the top of the pack back then, now not so much.