I've been using the Mexico Topo Atlas from Bicimapas for over a year now. I've used it on a legend e-trex, Nuvi 650 and for the last 5 months, on a zumo 550. It works fine on all three gps's. One of my riding buddies uses a Garmin Rhino and it also works fine. I've used it on major highways, secondary roads, urban streets as well as off road. I ride my atv on dirt roads and the map has been very accurate even off road.
It has happened in two or three ocasions, on mayor four lane highways, (two lanes on each direction) that my GPS shows my vehicle OFF the highway (about 5 or 10 meters off). This is due probably to the fact that the highway used to be a two lane road and the other two lanes were built recently, I think. Other than that, I've had no problems
If you have a zumo, it might help to do a software update. Garmin continues to put out update versions for this product.
Hope this helps.