I tour with a Garmin Edge 705, the previous high-end GPS model from Garmin. I'm not sure that I'd use voice guidance, but I do like having the 705 direct me along my pre-planned route. I find it especially useful in cities where the routing tends to be a bit more complex and you also have to watch for traffic. I've also found the arrival time estimation to be fairly accurate and useful. Riding through Big Sur, I found myself stopping to take pictures around every corner. When the Garmin started predicting that I was going to end up riding after dark I knew I had to be a bit more judicious with my time. When on tour, I try to charge the Garmin once a day, but realistically it could probably go for 2+ days without needing a charge.

I will point out that there are some limitations to the Edge 705. The screen is decent, but can be difficult to read if the sun is shining directly on it. Entering destinations on the Edge itself is a bit cumbersome due to the lack of a keyboard. It's routing is about what you'd expect from a computer: it will get you from Point A to Point B, but it won't necessarily pick the most scenic, car-free (or flat!) route; this is why I typically plan my routes in advance and upload them to the Garmin before leaving. Finally, on the Edge 705, there's no easy way to return to your starting point via the shortest available route. If you're 28 miles into a 30-mile circular route, the "Return to Start" function will have you riding the route for 28 miles in reverse. Your only options are to enter the starting address manually or to save the location before you start riding. This isn't really a problem for touring, but when I get caught by rain the middle of a training ride, I'm always annoyed that there isn't an easier way to get home!

In the end, I'm a big fan of Garmin's GPS-based bicycle computers. Then again, I'm also a fan of disc brakes, 10-speed drive-trains, and wouldn't use a Brooks B17 for anything but a penny farthing...