The Magellan Mio/Cyclo 505 is a stunning "okay". On road, if performs fine, for the most part (you can have a map screen with two metrics on it, if you care to set it up; I do heart rate and speed--or distance, if I'm counting for cue purposes), but the [OS] map hasn't been updated for a while. Not really a problem, if you're following a track. Off road, is another story. The unit fails pretty spectacularly in tight, twisty tracks--it will often assume you are going the wrong way (this may be related to the electronic compass?), and tell you to re-route for a few hundred feet, until it realizes you are actually on the right trail. Mid-track re-routes are okay, for the most part, as long as they are obvious to the unit (like, a few hundred feet, it will realize what you did.). I can tell you personally, between the default 'zoom-the-map-way-the-hell-out', and the quick snap to large view from small when you hit a direction marker, it's very easy to miss turns that are within a hundred feet of each other.

Unfortunately, I find, short of Google Maps, very few devices/programs can be used reliably without a cue sheet, and even so, I prefer to 'scope out' the route by map.

I could gripe endlessly about the start/stop issue with the Magellan unit. At the end of the day, it doesn't really matter, but it's irritating, that after loading the bike/milling in a small area (20 square feet) for 10 minutes, it doesn't pause recording. Yeah, it's my fault, yadda yadda, but losing a track because I forgot to turn it off for the highway kind of sucks. At least some sort of program recognition would be nice. During a ride, if I'm not moving for a few minutes, it does pause by itself, but as you noted, if then prompts, "start recording?" after a hundred feet, or so. My $60 Sigma computer was smart enough to figure that out by itself...

I can't speak to the Mac vs. PC issue, so...