The UCX works perfectly. It's so simple to set up and maintain. You're going to love it.
Voice quality on any voip is really a function of bandwidth and the availability of QOS. If you have 5Mb upload, you're not likely to have any issues at all. Even if you use G.711 codec settings, you could technically have 50 simultaneous calls so I wouldn't worry too much. Packet loss and jitter are what you want to worry about.
I have a few customers who have in excess of 30 IP sets at multiple locations with 6Mbps connections at each and they never complain of voice quality (or anything else for that matter). They just love these systems.