A few tweaks to how they (Blizzard Groups, specifically) work would vastly increase the chance of the program being used by the playerbase at large -- interestingly, the one feature set that would be absolutely specific to Blizzard Voice (that being in-game management), and also the biggest selling point, is entirely absent.
Be sure to wait a few moments after hanging up before making another call.—Collect calls are not billed by your long distance company, but by other carriers, and most often from a pay telephone.
Right now it's a not terrible substitute if you couldn't use discord but I see absolutely 0 benefit to switching, and personally preferred the convenience of the last messaging incarnation of bnet.
It's not a total failure, but the fact it's a beta is inescapable. If you want voice quality you'll still be on TS / mumble or something else even over discord or blizzard voice.
For example, you won't need to know a contact's Skype username to message them, you can just use their phone number.