Not all flip flops are equal.  The flip flops that are completely flat and are made of a cheaper material may give you a tendinitis or activate heel pain/plantar fasciitis due to the lack of support.  They may also cause blistering if you walk long distances in them. However if you can find one with a good arch support, that is not completely flat, and made of a more sturdy material, then we recommend that type of flip flop to wear.  A better constructed flip flop sandal will lead to less incidences of blisters, and tendon and heel pain.