Seems like a very good deal. Recommended price seems to vary from store to store but it's around £30 and I can't see it cheaper than £10 anywhere.
Link seems to be a bit flaky, here's a direct one:http://www.newitts.com/product/IT022842/Adidas_Boxing_Box_Ball.htm
The Adidas Double End Box Ball, floor to ceiling, has been designed with PU3G Innovation, to make the material appear like real leather yet helps absorb perspiration whilst remaining subtle.
-Maya 1.2mm 100% PU artificial leather.
-Changable latex shell butyl valve bladder.
-Nylon/elastic changeable adjustable straps.
-Complete with S-hooks and two triangles with screws.
-Size: One size only.