Geomags are great fun - from seeing how the sticks either attract or repel each other, to what shapes and structures you can build.
My little girl has just turned 3 and makes triangles, my 5.5 yo loves making cubes and pyramids. He also knows now how many corners, faces etc a cube has. great educational toy.
... and we parents love building more complex structures.
If your children are moderately sensible, they won't put the balls in their mouths - they do roll around a bit so the bigger issue is not to let them get lost.
A definite hit, in my view the ratio of stick:ball is too low, any good 3-D structure has several sticks meeting at one ball. This could be to compensate for losses, or just not thinking through how people will play with them.