This all depends on what your specific needs are. Do you just want something that can plot a route on roads to get you from point A to point B? If so go with a car system mounted to your handlebars as many now have a "bike" mode. If you just want a map to see where you have been and you can find your own way around, you can use a lower priced handheld for these tasks. If you want to preplan routes based on a site like mapmyride or you want to use HR and cad, you will need to look at the more expensive units.

I personally love my 705. I preplan rides and this has let me get out onto more routes than I think I would have without it. You can use a paper map, but just following the line is a really nice feature.