My little girl was given a pack of these for her birthday (1st!) in September.
At the time we thought they were a pretty poor present from someone with little idea about what to buy a 1 year old, but after giving her a bit of freedom to play with them they are actually quite a good toy.

So, this is a thick but soft moulded plastic carrier with a zip closed top which carries 70 different sized interlocking coloured bricks. Essentially these are Duplo bricks (oversized Lego) under a different name.
There are a handful of square 'base' blocks which for quite sturdy platforms to build upon, then various heights of 1, 2, 3 and 4 long strips.

My little girl is now 15 months old, and so still not able to lock the bricks together, but she is able to stack them in small towers, though I have to press them together.
For the most part she uses them with her other toys - mainly bashing them against different things to see what sort of noise she can make! However, when she becomes bored and just wants to chew, these large plastic blocks are perfectly safe.

I have been using the bricks to teach her colours. We separate them into their respective piles and ask for a green or a yellow brick to see if she can differentiate between them. She is beginning to respond to this in a manner, but is still a little young for those sorts of games really.

Her favourite game with these is knocking down towers which I build for her.
While her coordination isn't advanced to the point that she can press them together, she is superb at separating the individual bricks and happily spends half an hour pulling them apart until none are connected.
A slight worry is that she is obsessed with the empty plastic pack they come in. We have to tuck it away out of sight and out of reach, because on the occasions she has got hold of it it's all she wants to play with! Obviously she is never left unattended, but it's still a concern.

In summary, the bricks are clearly on the verge of becoming one of the more played with toys, but I think 18 months+ is going to be the optimum age to play with them. The bag does say 1 year plus, but I think it's a bit young to get anything out of this toy.

For the price, these are good value. £15 seems to be a fairly standard price, with some of the big chains asking as much as £20 for this starter pack.
As I say, I'm sure these will be out constantly and will be added to (there are lots of add-on packs) in the near future.