This usually sells for around £16. I had my eye on it for a while for my Daughter's birthday, reserved one today at Argos Beckton for £16.99 but store closed by the time I got there. I then checked with Smyths but they didn't have any so decided to try Tesco and fortunately found it there. It wasn't until I took it to the till I realised that they are selling it for £3.75 so decided to buy 2.
This may be a store specific deal at Tesco Beckton. There are still a few left and the price tag was showing £12.50 so people will not be aware of £3.75 deal.
Instore deal - See link for more info on set only