The Teasi works fine, but I don't. It's bitterly cold and foggy here, and as I live near the bottom of a brook valley, there's quite steep hills very early on on a ride unless I want to go into or out of the centre of town. I just couldn't get in the groove.
The Teasi works well, I would say, though I have nothing Garmin to compare it to. It uses OpenStreetMaps, but I've read that it will accept another format, so I plan to investigate getting OS maps on it. Entering addresses is simple enough, and it beeps loudly on turns. It also pairs easily with my BTLE speed and cadence sensor. No Strava integration, but I don't care about that. It'll do me.