They have really big bumps and lots of them inside.  Then the raised part under the toes is not too comfortable for someone with uncommon foot shapes.  They are probably really good once you get used to them.  I just looked inside the worn-out pair I have.  They are smoother.  I think they vary in the interiors quite a bit.  I bought a pair of these, but returned them due to them being too bumpy.  Mine are so old now, I don't know what they were like new.