Technical pros and cons. They way it works is that when you use their login you get prompted to register with them, which is done using a phone number. From what I understand they do not keep the phone number, they just send my site a token that says "yep, this person = that phone number"
Sorry - my company is an audio social network. Because we don't use a camera for our live streaming many of our members tend to be shy and possibly privacy focused.