Rather than immediately get upset, after a lot of checking into things and sources, I found that the units are exactly the SAME in audio quality, and because the unit with the mike is more popular the other seems to be an issue to get. I have worn the Isotoner Terry Ballet Flats for so many years I cannot count. These slippers fit different in the beginning. I?m a size 11 and neither would fit on my feet so I?d guess even the bigger one is a size 10, if that. Quick Delivery! Can be worn with jeans or a dress! Also melted our duffel bag and left melted plastic on her clothes. Very disappointed with the sizing! The sound is fantastic, and the option for hearing ambient sound or turn that off is a great feature. I dont have any room to spare for the fit.