There is a lot of information on end plates from Ed Moorman on this site that suggests the end plates will help with roll rate and stability. Those plates come off easily with 2 2-56 screws. Can fly with em on or off real easy. They are real light too. 3/16" balsa.
I don't like the round wing tips look, and Ed's research shows they are one of the worst aerodynamically. So that made it an easy decision to cut them off. But with the wingtips flat, it didn't make sense to keep the stab rounded so I left them square also. I like the look with squared off better. Just a matter of preference.