These blocks are a great idea for the preschool crowd, they are just like the magnetix but are much larger. This is nice because you don't have to worry about them being swallowed. However, there are a few problems with the concept.
My girls love to build with them, but do get frustrated. Since the balls are bigger they do weight a little more and make it difficult to build 3-D objects without some minor engineering knowledge. Another downside is that you need at least 24, if not 36 blocks to be able to make anything substational. This makes this a very expensive toy since you need to buy so many for the imagaination to go wild.
Overall I would suggest these if you are looking for a magnetic kit like big brothers and don't want to worry about magnets geting swallowed. If you decide to get them as a gift buy at least two of the twelve packs or one of the larger packs.