Using Fabric - digits for mobile number authentication

I have some specific questions -

How is digits for signup/login via mobile number?
Is it trustworthy(I have read that twitter have used fabric as a data collecting mechanism in the past)?
What are the prospects that it will be free forever?

Solution

Yes, Digits gives your mobile app users with simple phone number
authentication.
Yes, it is trustworthy, Fabric is now part of Google and Google is what your know.
Yes, it is free of cost.
https://twittercommunity.com/t/is-digits-is-completely-free/64909