This is a set of maps for Garmin GPS units that's…
Price Paid: $90
This is a set of maps for Garmin GPS units that's also usable with Garmin's (free) BaseCamp trip planning software (BaseCamp runs on both Mac and Windows). If you don't have a Garmin GPS, you are NOT interested in this software (I suppose you could use it just for trip planning on your computer, but it would be awfully expensive relative to the competition). These maps offer detail "similar to" a USGS 24K (7.5 minute) map for your GPS.
My review summary is: I'm glad I got these maps; they have been very useful and fun for me, because I do advance trip planning on my computer, because I use my hiking GPS for driving as well, and because I really only go hiking/driving to remote trailheads in California. If I traveled away from the West Coast on a regular basis, or I didn't do trip planning on my computer, I probably wouldn't find this as worthwhile.
First, why buy the maps at all? You can get topographic maps for Garmin GPSr's for free, from places like GPSFileDepot. So why would you want to pay $$$ for this? I can think of 2 reasons:
1. Routable, reasonably up-to-date roads and trails. The free topographic maps on the Internet don't have routable roads (you can't say "get me from here to point B" and trust that the GPS will give directions) or trails. While you should NEVER trust the GPS completely, it can be *very* nice to have this data, especially when you're trying to get to somewhere deep in a maze of Forest Service roads. You can even get free routable maps (check out Open Street Map), but at least where I live, the quality of those maps is dubious once you get off the main highways. So this is a very nice feature.
2. DEM (elevation) data. This is nice to have on the GPS, so you can get an idea of what the trail you're about to tackle looks like in terms of elevation gain. On a computer using BaseCamp means you get to use the whizzy 3-D view, which turns out to be more useful than I ever thought.
Garmin offers its 24K maps in at least 3 formats: DVD, micro SD card, and downloads. You want the DVD. Why? The microSD card can only be used on one GPSr at a time and can't be used with BaseCamp. The download can't be used on a computer at all and you have to buy a microSD card to hold it. The DVD, on the other hand, offers more coverage (4 states vs the 2 on the microSD card), and can be used with both BaseCamp and the GPSr.
OK, so that's why you should buy this and what form you should buy. However, this is not a perfect product. The two big issues that I run into are:
a) "Similar to" a USGS map is not the same as "looks like" a USGS map. If you want something that looks like a USGS map on the screen of your GPSr, this product isn't it. It will give you detailed contour information, place names, river and stream information, but it will only 'kind of' look like a USGS map.
b) Trail data is VERY mixed. For areas I'm familiar with, the trail coverage is quite good and accurate in the Sierra Nevada. In the San Francisco Bay Area, and up and down the California coast, it's much more spotty. Sometimes it's funny: the trail data in Pt. Reyes National Seashore magically stops on an east-west line - north of the line, nothing; south of the line, trails, and this bisects some of the most popular trails in the park. The good news is that Garmin offers a tool on their website to let you view the 24K data, so you can figure out exactly what you are and aren't getting.
After upgrading from the free maps, I'm really happy I did so: the Garmin maps have really provided a lot of usefulness to me over the free ones. A viable alternative for someone who doesn't care about routable trails and/or travels a lot more would be using Garmin's City Navigator (for road maps) and free topographic maps -- roughly the same price I paid for the West Coast would give you roads for the entire USA.