They also can be made by Perfecto/Marineland.
I agree that they seem to be of lesser quality. I bought a 120g Perfecto made Top-Fin in 2004 for my freshwater planted tank. I drained it down for the first time a couple weeks ago to convert it to a reef tank. It was then that I noticed that the seals were clearly inferior to what my AGA 180 has.
The tank never leaked and I didn't think it would when I refilled it, but I resealed it anyway just in case.
So I don't think that you'll have any problems with top-fin, it' just not as well made as the actual brands.