Well, I believe they have “guaranteed” the divi for 2019 too - but yes, beyond that, it will have to be earned rather than entitled. Nothing wrong with that, 'tis the way it should be, and a divi policy linked to FCF makes much more long-term sense than any earnings basis.
Around £15, I agree, there probably are quite a few better places for your cash - though that it is more of a reflection of the ever-larger number of compelling long-term opportunities out there, whatever the near-term overhang.
And… not a few WORSE places for your cash, too. I remain a happy holder - whither goest the dividend!