I'm a huge fan of WhatsAuth! We've been using it over at sosafeapp.com, and boy, has it made a difference. Not only has it significantly streamlined our sign-up process (our conversion rates are smiling), but it's also made a noticeable dent in our costs.
The biggest win for us has been ditching the SMS validation - an expensive affair and an often frustrating user experience. WhatsAuth is a much cheaper alternative and, to our surprise, has proven to be more efficient.
In short, WhatsAuth is a game-changer for any business looking to improve their user sign-ups and save on costs. It's a no-brainer in our book, and we highly recommend it!
