Indeed - it is resistive - hence I'm not being too harsh on it. I think it will be perfectly functional in use. To be honest, I doubt I'll be pecking at it much on the move - I tend to just ride and look down when I've got a route change - I think it will manage that pretty well.
Readability is hard to judge - it is backlit so it won't be an issue in the dark (making the heroic assumption that it will light up at turns) - its not got a very wide viewing angle but again, mounted on your stem, this isn't an issue. Just popped out to look in sunlight and it seemed fine.
Screen size is good - certainly the UI doesn't seem cramped and I can set up the data screens to be readable and clear. Then again, I don't like to clutter the screen too much, just time, distance, speed and cadence as a rule. The smallest data field seems readable.