Absolute rubbish. We do a lot of Lego in this house, both myself and my husband were big Lego fans as kids and my three kids love it too, so we're pretty good at putting things together. My 8 year old son was bought this toy as a Christmas present and we wasted four hours this morning trying to put it together. He had spent several hours at it yesterday and couldn't build it, even though he can always do Lego sets by himself, and I told him I'd help today. No good. The Lego-type bricks will not stay together and as the previous review says, if you finally do get to put a piece or two together, when you try to add something else it falls apart again. I was seriously considering Superglue.
I loved the original Knex set which we bought for my son a few years ago, and which just consisted of the plastic shapes which click together with rods. The brick aspect of the sets though are poorly made and it's very frustrating for children to not be able to put these together.