On the flats and with the right rear wheel,the Gebee will undoubtedly shine,changing sprockets is supposed to be quick&easy also,beats roller drive in wet conditions,is efficient too.
Learning to get along with the belt drive reqs. some expertise.
In dry places without bad hills roller drive makes sense,cheap too
Forget about changing rollers on the Staton,has cent.clutch,DE is much better, easy access to roller.Also has engine lift-off feature that,people either don't seem to mind, or profess to like.
Staton is durable but on the clunky side,heavy with boat-anchor gearbox.NV version is unbeatable in places with steep hills,but it's pretty heavy,expensive too.
These dual-drives are intriguing,what engines are you using 5-7?,couldn't you use larger rollers? if you ran both engines all the time.You could conceive of a mainstay drive for the flats and if you have to climb, kick in the auxiliary fairly 'low-geared' drive to help out,getting it running might be the problem (seems to rule out Staton).