I had a pair of these Birkenstock Milano shoes and liked them very much at first.  After standing and working on a concrete floor for many hours a day an an elementary teacher I began to have trouble with my sciatic nerve up the back of one leg. 

 They strap also bothered me some.  I have varicose veins and the strap irritated the ankle veins.  I experimented with other shoes on the concrete floor I walked on a lot and found that shoes with an athletic- type sole and Crocs seemed to absorb the shock of hard floors like concrete much better than shoes like Birkenstocks with a harder sole....