Although its feature set is tailored for geocaching, this unit should work well on a bike. I won't try to evaluate the price, as you can do that with the Web's price comparison sites.
If you have not yet found it, see the review at http://www.gpsinformation.net/waas/Mag3-D/eXplorist.html
and while you are there, look around the site, which contains just about everything GPS and links to the rest.
The rechargeable lithium ion battery would make me think twice about this unit for trips of more than two days away from a wall socket. If those are in your plans, you would need some fairly expensive replacement batteries to keep going. Many competitive units use AA cells, of which a two-week supply is easy to carry on a bike and which can be bought everywhere in the civilized world.
A few people on the GPS newsgroup have said they built a four-pack of rechargeable AA cells with which to recharge the built-in LiIon battery. Extra fuss and extra weight, but probably fine for occasional use.
Is that map set the new Topo 3D USA or the older Topo USA? There is quite a difference, which you can check out at http://www.gpsinformation.net/waas/Mag3-D/Mag-Contours.html
The biggest decision when buying maps and a mapping receiver is whether to go for auto-routing. You should at least consider substituting or adding an auto-routing street map. I used direct routing--straight lines between waypoints--on my bike for four years before buying the feature, and now wish I had done it sooner.
The Adventure Cycling waypoints are set up to work with direct routing. Auto-routing adds detail and prompting to this. It's comforting to see "0.2 miles turn right on Hillsboro Rd" but hardly necessary.
Auto-routing makes building your own routes easier. Set the start and end points, then add a few intermediate waypoints if needed to guide its little brain along the roads you want, rather than what it first chooses. If that appeals to you, please check whether the Explorist 500 and the maps you pick will allow intermediate waypoints. Some Magellan models do not, but I have not heard about this one.
Finally, ask questions on the Usenet group, where you can probably find more people who are using this gear. It is sci.geo.satellite-nav, accessible through Google Groups or your own newsreader.