I have not used one, but reading reviews by people who have, I am skeptical. It gets good marks for its intended use in an auto, but for cycling, there are some questions to be answered:
Not waterproof, so you would need a case.
Rugged enough? Cannot tell from spec sheets, but would want to find out before putting it on a handlebar. No handlebar mount, though RAM could probably cook one up.
Battery life measured at 4-1/2 hours in one review http://www.brighthand.com/default.asp?newsID=12573
It is a custom lithium ion battery; plan to buy a spare. Both batteries need recharging every night from a wall outlet.
The TomTom maps and mapping program are well regarded for auto use. It is good at here-to-there navigation. But can it build a route containing several intermediate waypoints (vias)? Can it be told to ignore interstates and toll roads? Check these out in your owner's manual.
As for other items to look at, the hand-held receivers that use AA cells work better on a bike. Garmin's GPSmap 60CSx is popular. Browse this forum and check out http://gpsinformation.net/
for reviews, discussion, and comparisons.