Don't have the 521 Keith, but do have the 541s - which is very similar to the 521.
Perfectly suitable for what I need it for. I highly recommend that you also spring fore the Blue Chart Vision card for the area you boat in - makes a big difference. If you have a VHF radio with DSC you can wire the 521 to it so te GPS feeds location to the radio so if you have to press the Come Save My ***** button (DSC) your location is sent out with the call.
Also, if you have separate batteries I'd recomment that you power the GPS from the NON-engine starting battery, because, you see, if you power it from the start battery the unit will shut down every time you start the engine due to the current draw. (GPS monitors batt voltage and automatically shuts down to prevent draining the batt). Under certain circumstances it could be a PITA; like when tubing/skiing when killing the engine to allow people on/off the boat safely is frequent.
Dan
EDIT: Forgot to mention - I spent HOURS price shopping for my GPS, VHF, antenna, and the replacement AM/FM/CD head unit, and listened to recommendations. I went with BOE Marine.
http://www.boemarine.com/ You MIGHT be able to find it a little less expensive else where (but not significantly so; they had the lowest on the GPS, but the VHF was 10.00 more than cheepest, stereo was 2.00 more) but BOE's customer service is fantastic.
garmin gps 521
Linear Mode
