Not really a big fan if this toy. I know I lot of the reviews state that the adults play with it half of the time so I'm sure that assist in the rating. I will say off the bat though that my kids (3yr & 18mo)do love playing with it for a good few minutes at a time but mostly as a colorful ball toy.
It stands about 12" high when stacked/assembled. The balls range in diameter from about 2", 2 1/4", 2 1/2", 3", 3 1/2", 3 3/4" with the 4" base. Again those measurements are really rough, but it's just for a general idea. I'd say that they are weighted in the bottom center of the balls base, but not magnetic from what i can tell. Just given the shape when tucked into each other and the small weight might give that impression though. The balls are assembled with the top half(cup) and lower half(ball). The top half has a very slightly rubberized coating all except for the smallest ball.They are light weight balls but you can feel the presence of the balance weight. I know because they are a ball shaped toy most kids might be inclined to toss them around accordingly and for that I wouldn't rate them durable. My kids haven't tested that limit yet, but I'm sure it's a matter of time until it goes Humpty Dumpty right into the wall.
They state that you "can stack, spin balance, open ended play". Honestly from practical play at the young toddler age, they can stack it directly on top of one another very still and it will stay piled, that's about it. I played with it myself initially to check the limitations/range of stacking play and really the second product picture is about the most staggered you can make it before it topples all over the place. You can roll it, because it's a ball shape, and yes like a ball you can spin it too, imagine that, a 'free extra feature' ;) I've tried to stack these outside of the base with no luck, of course, and I've tried to stack them inverted(cup side down, one on top of another) with no luck there either. Again if I approach it as meticulous as one would while disarming a bomb then I can get a couple different configurations out of it, but my kids with more of the 'pull the pin and launch' grenade style leave little else for this toy to do but to stack it straight up.
It's colorful, it's a nice idea and the weight is a nice touch. If that weight was in fact also slightly magnetic, this might be worlds more fun with far more range of play. Being that it's not easily stable or all that durable(for 'ball' type abuse)and really nothing more than a plastic stacking toy, I think it's overpriced. I would have paid $12 for this at Imaginarium or a store like that. My kids do love it though for the few minutes at a time that they play with it so, I concede to their authority, and don't pretend to understand why.