I have the cheap tomtom. It's the only one we've ever had so I don't know how it stacks up againt other $150 units.
I only have two dis-likes about it so far. (4 months using it)
1) When you first turn it on it sometimes takes 1.5 minutes to figure out where you are. I did an update which helped some. Still take a minute or so.
2) In motown and during heavy traffic I take some backroads. All paved mind you. But tomtom is useless in those situations. It would steer me straight into the heavy traffic roads if I followed it's instructions.
In the last month I went to Oklahoma twice and it worked perfectly on both trips.
He who is enslaved to the compass is free to sail the seas