I've a Nuvi 550. ( Very close to the 500. )
Seems to be ok! The screen is smaller than my Nuvi 750 but close in brightness.
My one complaint is, the map background is green instead of white like the 750.
Hard to see secondary roads ( in gray ) against the green.
I run it in night mode ( black background. ) Roads show up better.
The RAM cradle is set up so you can't remove the Nuvi with out unplugging it first. It's hard to find the plugin socket when reconnecting it. ( Mine is using a RAM mounting setup on the bike. ) Can't see the socket when reconnecting.
If you want water proof GPS with out spending a lot of money, the 500 / 550 is ok.
Zumo's cost to much for my pocket book.
I've a map program from several years ago that has older (abandoned) roads on it. I can load the second mapset and switch between it and original mapset that came loaded with the Nuvi. So if you have another map set, you may be able to use it as a second mapset.
My RAM Mount... http://powers31.info/NX250_Instrumentation.htm
On my NX250 "Back roads explorer"
2017 Yamaha XT250
1990 Honda NX250 (Green/White)
2011 Kawasaki KLR 650 (Orange & White )
My KLR Page..http://www.powers31.info/2011_KLR650.htm
Mod's to KLR:
Power socket, L.E.D. Battery Indicator, Camera bag holder
Custom Saddlebag frames .
Louder horns, Firstgear Onyx tail bag.
Custom Aluminum Skid Plate.
Cut down seat with Custom pad.
Go Pro Camera mount.