I wish the motorcycle specific GPS unit's were a little more reasonably priced. Hard to justify paying triple for something that does the same thing!
I got my nuvi several years ago for about $125 and a Montana this year for more than 4 times that.
But they DON'T do the same thing.
The Montana is not only easier to see in ANY kind of light, but the menus are easier to use. I can build a custom main menu with items from down in any of the regular menus. Then it is waterproof, shockproof, has a powered mount, and has another camera. (My camera-only camera developed a spot somewhere inside it while riding through Saskatchewan.)
The Montana will also "backtrack", display tracks, build routes, supports imported routes, and a host of other funcitons that my $125 nuvi never did.
I'm not trying to say that over $500 is a reasonable price; I'm saying only that the Montana does more and does it better. (And a powered mount with a real 12V power connector.)
The photo shows both the smudge in my "real" camera (in the spruce trees above the mirror stem) plus the readable GPS screen even though it's reflecting my brightly-lit high-viz jacket.