I had been wearing a pair of clogs to work (standing for almost 8 hours a day).  They hurt my back and feet even though they were purported to be a "comfortable working shoe".

I bought the Birkenstocks because I wore them as a teen.

They are great!  The negative heel thingy puts me in the proper posture so that I do not strain my neck and back.  There is ample room in the toe so they are not squeezed and they look great!!!