The 8MB is enough for a few counties worth of data, but that's about it. The topo maps are pretty data-dense, so they eat up memory quickly. The Metroguide city maps are smaller memory-wise, and cover wider areas, but I still couldn't get the entire 250 miles of interstate from Fargo to Minneapolis on. That was my only major complaint about the Legend. The other drawback is that you can't have both types of maps onboard at the same time.
I really liked my Legend, but I just recently got a great deal on a Legend Cx, with the expandable memory. The stock 64MB card is enough to hold all of ND in Topo and Metroguide, and you can switch between them at will. I'm keeping the older one as a backup GPSr. I can't say anything about the Magellan, as I've never used one.