I dont wear flip flops often so Im thinking that the skin in between my toes are not seasoned enough. Luckily, returns on Amazon are easy. This isn’t as powerful as another one we have. The voice clarity is also not as good as my Plantronics voyager focus UC. The casters used are single ball bearing on the swivel end, the caster itself is on a steel shaft. The 8s fit like a true 8 on me, but the 9s felt like a 10-10. Crossbars fit perfectly and took a total of 15 minutes to install. This is a little expensive for the level of trainer. With the name “MEGABOOM” one would think there would be a significant upgrade in the bass department as compared to others. 4 stars because I have just bought them but the fit and feel .