We have a TomTom, and I like it for the most part. We do call it the DumDum sometimes. I know someone who has a Garmin, they call theirs the Gremlin.
I have figured out how to make DumDum change it's route for me when I don't want to go the way it wants me to - it does it automatically. I like that. I do not like it when it yells at me for speeding - I had to drive in the Detroit metro area (696 interchange) and it's a drag race there - I was going 75mph. It kept gonging at me, scared me the first time. I don't like that.
I have done one update on it, and that was free. We don't pay a subscription. I haven't updated it recently.
I like that it tells me about when the turn is coming up, and that I can see the picture to see about where it's at. That is nice. I like the estimated time of arrival thing.
We didn't really research them fully, DH bought it when he was down south because he needed something to get him to the job sites, since he didn't have a map or anything. The TomTom was on sale, so he got that over the other ones. Thus far, it has been an "expensive" purchase that we have used and been pleased with. (We do not do the whole "lets buy expensive electronics just because thing - we have older cell phones, ancient radio, old game system (PS2), and don't buy new things like that. The TomTom is the most "advanced" we are).
I think if you will be driving to unknown places often, it's a great idea. DH uses his a TON when on storm work. He calls to dispatch and they say "Go to 1234 Main Street in Wixom" and he has to find it. Before, he had to use a map and search it out, now he just punches it in, and goes. I'm going to use it for the first few weeks on my new job because I have to drive to over 100 different stores over two weeks, and the last thing I need is to get lost. I can use it to go from A to B, B to C, C to D, etc, which would be a PITA to figure out on Mapquest. If you are just using it to go from home to a new place, once, I wouldn't think it's worth it. If you plan on using it to travel about in a new city, then yes, it would be nice.