I used ReadCube several years ago when it was still really new (and free). Great program, very pretty interface - but it didn't work on Linux. When I switched from Windows, I had to let it go.
I mostly use the web version, and that seems to function well everywhere these days. Not sure about the desktop version, but after ages and ages they are finally getting the desktop application that incorporates their Papers acquisition, so it might be worth looking again if you like it. Hopefully, that does a better job on Linux, but that's always a gamble.