Like someone else said, these blocks are barely magnetic. If I connect two cubes and lift the top cube, it does stay together, but only if I lift very carefully. It's very easy to accidentally knock them apart.
What's worse, the cubes are exactly symmetric and there is nothing showing on which side the magnet is. If you want to connect two cubes together, you have 1 chance in 18 of connecting the sides that (a) actually contain magnets and (2) have magnets of opposite polarity so they don't just push each others apart. With a toy intended for children I'd expect it to be far easier to find a way of actually "snapping" the blocks together.