My mom swears by the Shape Ups but I can't wear them because the heel is too loose.  She has wide feet and they are great for her.

I tried these as an alternative and they fit my narrow, low-volume foot really well.  No slipping in the heel.

I was recovering from an ankle sprain when I tried these on and because they are so lightweight and flexible, they didn't pull on my ankle or make me feel unstable the way the Shape-ups did.  The foam that the sole is made of reminds me a bit of the croslite in Crocs.  It gets compressed some and with the articulated sole, it ends up getting pushed up into the arch of your foot as you walk.  It's like having extremely good arch support.  I've never EVER worn a shoe that supported my arch like this, in fact.  I would imagine that it could be uncomfortable for someone with flatter feet.

The overall form of the shoe is more lightweight and flexible than Shape-ups.  It probably won't prevent pronation inward.  The slight rocker motion (much less than with Shape-Ups) causes me to hyper-extend my legs a bit with my stride.  I'm hoping it doesn't cause me knee problems.  It would be nice if these stabilized the foot a bit more.

Because these support my arch, I don't have the forefoot ball pain I was having in all my other shoes.  It transfers a lot of the weight into my arch.  They don't feel as cushiony inside as the Shape-Ups did.  When the weight is distributed well, you don't get the hot spots where you need the cushioning as much, though.