I purchased these for plantar fascitis.  Unfortunately these things feel like a concrete slab was poured into your shoe.  Even after wearing them for a long time, they never really softened up that much.

While they have helped the plantar they never completely solved the problem.  I started using New Balance motion control sneakers (model 1123) and they have helped dramatically.  Most importantly the NB are firm yet cushiony unlike the hard as a rock Birkenstocks.  The Birkenstock sandals provide more cushiony support.  The insoles and shoes lack the necessary support!