A good thing
Both the deal and the utility are good
Not needing to own/top-up an Oyster Card is incredibly handy, just use a contactless Amex or Mastercard or whatever - same card for in and out, and the prices are capped as with Oyster so you never pay more than the equivalent all day travelcard. It's a case of technology being used to make life easier and better, and if other cities don't have this yet, they'll want it.