Creator of Radiant Player here. Performance and memory issues were a problem in the past and unfortunately have resurfaced in the latest release (1.4.0), but I am looking into them!
When did you try it the last time? I never had stability issues with recent versions. Sometimes (very seldom) it ends up eating 100% CPU, but restarting it fixes that.
Very nice app but I uninstalled after awhile because I want to get rid of Adobe Flash Player. It (the Adobe software, not Radiant Player) kept asking me to update itself...
http://www.sajidanwar.me/radiant-player-mac/