Not bad, much more economical than the real thing!
It's a bit clunky but basically works. Would be great to see it updated for touch interfaces. I believe that actual, 3-D manipulatives provide a much richer learning experience but this is a great substitute when needed due to space, budget, and time (to obtain better materials) is an issue. I love that it includes a huge variety of manipulatives all in one program. I would greatly appreciate an offline version for classrooms with no internet access.
How I Use It
Basically the same way you'd use real manipulatives! I don't bother much with things like shape tiles that really are much better to play with in your hands, but for other things like base-ten blocks, fraction tiles, and such, it is great for illustrating and demonstrating concepts. You can let kids try things on their own, such as proving whether fractions are equivalent, and yo never have to worry about not having enough pieces, losing pieces, and cleaning up!