I had one that I used for a few years. (I think it's on my shelves now, as an emergency backup.) It worked okay, but was a little bit fragile. You had to be very careful when opening it for cleaning. Finding spare parts is difficult. I think you get what you pay for, and SunSun filters are inexpensive.
I have one not in use anymore. Used it for about half a year and it started leaking. Not even after a cleaning. Just sitting there working and decided to start leaking. Replaced it with a used FX5 and have had no problems for over a year.