The sign up used to be 50% up to $30 but it's recently dropped to just 10%, although I referred someone recently and it didn't track so they contacted CS and ended up with a 100% bonus. Make of that what you will.
If can be combined with RAF which pays the referrer $25.
I'm happy to refer anyone and split the RAF bonus but the 10% sign up bonus isn't great so severe underlaying or even just signing up to get the RAF and forfeiting the bonus may be worth considering