As far as I know MBNA are the only ones who issue them. You generally can’t use them in shops as they don’t come with a cheque guarantee card, but you could if you were paying for a large item such as furniture that had to be ordered in for you & would possibly take weeks, so the cheque would be well cleared by the time the goods were available, or you could write to someone you know.
I doubt if many people actually use them any more, as most people use online banking, but an example of someone using them would be if they had paid a deposit on an item of furniture & the balance had to be paid on delivery by cheque or bank draft, & the person didn’t have a cheque book. People used also write a cheque payable to themselves & lodge it into their regular current account as a short term loan to themselves.
They are treated as a cash advance & the associated interest & charges apply. As far as I know they don’t charge the medallion stamp duty, but am open to correction on that.
I would avoid using them if I were you.