IME, the Remora Pro must be equipped with a Mag 3 pump (or larger) to perform decently. Mine works nicely on a 70 but I would love something more powerful. I did have a lot of trouble with it in the past. The included Rio 1400 is a terrible POS also. With the Rio, I would say 40g tank or less.
The PM HOT-1 is probably the most underrated skimmer ever made. It is *realistically* recommended for up to a 90 gallon aquarium. I have heard on Reef Central that it puts out 3 times as much gunk as the Remora Pro, despite using a little Rio 800. It has a huge reaction chamber, thick acrylic, an adjustment valve, and much more for about $170. Premium Aquatics has them. This is also the only HOT skimmer that's problem-free with no customer complaints.