As far as I know, they are only on IOS phones.

They pay you back when you buy crypto from their app.

The thing "they pay" is their own currency so they are bringing value to their token which is fine as per my understanding, people may disagree to what I say but agreeing to disagreement is same.

They are also having a poll right now for AMA with Binance CZ. You may caste your votes here

Vote in Binance Poll on Twitter: Chance to vote for Metal to be featured in an AMA https://twitter.com/binance/status/1091637368153501696