We use the Ubiquity Security Gateway Pro and have for over a year now issues with it's WAN Fallback. In the beginning it simply wouldn't Fallback at all, after lot's of Customer Service and three patches it actually did it's thing, but since then whenever the fallback happened our whole connection got instable until the USG is restarted. Once we even had issues because the USG thought WAN was down because it couldn't reach Ubiquity's Ping site (It was down) and so the connection started flip-flopping between two stable connections.

Besides that the Ubiquity Needle is now firmly stuck into the arm of our Admins and all the Network Gear we buy is from Ubiquity.