A practical introduction to basic electronic circuits, it is actually pretty cool. Robust, easy to use, the separate pieces all click onto a board and if you follow the diagrams in the instruction booklet, you can make lights flash and alarms go off and more. If you have a child who enjoys following lego instructions, they will like this. If you have a child who likes fiddling with things (like your phone or computer), they will like this. But probably not break it!.
P.s. The price of this on Amazon.co.uk fluctuates a lot. I paid £20 sterling, but its now £27. So I'd put it in my basket and keep checking, the price will probably go down.