Thats how I see it:
Keyfree bitbills could be a great means of payment for the average Joe's and Jane's, and help Bitcoin to become mainstream. As their (bitcoin) value is forever locked, Joe and Jane never have to check any blockchain. They just pass the bill like cash.
But for this to work you have to trust the issuer to repay the bill in fiat (or better in
BTC to your own wallet). GBP "I promise to pay the bearer on demand ...". So issuer has to hold the private keys in escrow. Probably could only work if backed by a established trusted institution. A bank? Pah!
PS. Actually this is no different from bearer bonds, just backed by bitcoin.