For almost every use, anything over 1Hz is overkill. There are few apps which will even read the GPS more than once per second, and if you're just doing general mapping and following a route it's more than adequate. Paying for more than 1Hz is a waste of money unless you have specialized software and are going to use it for specialized stuff which requires the higher refresh rate. Get whatever bluetooth GPS you can find on sale, and it should work fine. I have an F-tech mini solar GPS, which partially recharges itself from solar power while running in the windshield, giving about 30 hours of daytime use on a charge. It works well with everything I've tried it with, including my N800. I've also used a Garmin Legend handheld connected to a bluetooth adapter from PC-Mobile, probably no longer sold, and it works OK. The Garmin is an old model with only a few channels, so it has to have a better view of the sky than the F-Tech, but it works.