bought a couple of these a few years ago, cheaper via another store (aldi) these are slightly updated to breathe easier..
However, at £8.99 i'd wait & circle to see if they drop in price to around the £3.00 mark as they make excellent kids day hiking sacks.
My kid has been using one since she was in beavers, now cubs, & for school day trips, we often just remove the bladder.
The low profile works really well, comfy harness that is infinitely adjustable, hang strap, easily accomadates a 600ml sigg bottle or similar.
Probably worth checking out in the pocket as to whether it has a wet weather cover sewn in,
A lot less bother than that damn spongebob bag with poor shoulder straps that you will end up carrying, & cursing,
This is low profile enough to strap to your own pack if your kid overheats, but mine has worn this without complaint & takes it to camp with her.
Just a thought.