We have Lingo as a secondary carrier, we've been pretty happy with it. Only thing I'd say is keep an eye on how it affects your other Internet traffic if you do a lot of uploads and downloads... if you have multiple lines, Lingo at least can be a bandwidth hog, particularly on the outbound traffic, which tends to be a lower cap unless you have a symmetrical line.

Also, I keep a landline as a backup because Comcast isnt' 100% reliable. The good news is that Lingo can seamlessly forward on no answer to the landline, so even if the net connection goes down, the call still routes.