mine is a free lifetime update one - worth the extra cash so you dont have to keep paying for new maps.
i did have one that in the main was fine, but i couldnt seem to update it - can't remember why now, faults etc i think, but possibly also cost and being outdated ... i just carried on using it, but gradually began to notice stuff like roundabouts etc that it did not know existed, and itd tell me to go right into a brick blocked road or something.
i eventually bought a new one when i was hit with a speeding fine, because the satnav was telling me the old speed limit on the road, instead of the new 10 mph less one ... so i was travelling 12-13 over in stead of the 2-3 i thought ...