I've been using these shoes for two months now and I can say that the quality is top rate.  Every part, including the stitching, feels solid and gives the impression that they will last for a long while (we'll just have to wait and see if that bears out.)

As for the muscle strengthening and posture control aspects, I think they do put a lot more stress on the calf muscles so they get a good workout.  And I do tend to walk more upright but that may just be because I'm thinking more about my posture as I walk in them than I would in another shoe.

Long and short though, I would happily buy another pair.