I don’t think you can use it on mobile devices other than the Lowrance devices, which is a shame.
However, as a piece of software to use on your PC, and then upload and download routes to a GPS, I love it.
It’s really quick for planning really big rides across a large area, like say the Welsh Ride Thing, where you link up a suggested list of points on a map, with Quo you can immediately see everything, and even have an in-sync Google Earth view so that you can see if the bridleway on the map actually exists on the ground.
Plus the file system is good for keeping stuff organised, multiple versions of the routes etc.
Probably best for a map geek, you could just use Bikehike.com for simpler routes (in fact my friends manage with this for planning big rides too), but I like the speed and flexibility of Quo.
Downsides are as already mentioned there is little mobile support, and that it can work out a bit expensive in the long run if you buy lots of tiles, but that’s the choice you pay for flexibility in which tiles you really want.
The software is free and a couple of tiles is only £2 so I recommend giving it a go.