These have been kicking around for a while but now they're cheaper. I saw one today in the Ivey bridge, Twickenham store with the shelf label reading £19.97.
I checked their terminal (that was logged in) and it said there was 1 in Twickenham with 2 on hold. 1 in Kingston Clarence street, 1 in Wimbledon, 1 in Hanworth.
I then got confronted by staff so decided to leave.
I hope this helps someone.