I have a TomTom One which is almost the same unit as the Rider. Its has soild basic NAV with a really good price. If you are looking for just Nav functions I would recommend TomTom, if you are looking to do more with it like geocaching or topo I would suggest a Garmin unit.
Oh on a side note TomTom runs linux and there is an open source project
http://www.opentom.org Who knows what there guys will come up with for TomTom