The fit in your ears (yikes). The quality of the cord (Ummm). The retractability of the main component (fail).
Sound quality is at best, average.
If you buy these, it's more about the look of having them... Mine have been sitting on my desk after only one, not so pleasant, use.
Laziness is the only reason I haven't returned these. I will never use them and I would not recommend.
The product discription says they have a built in microphone for calling capabilities. Am I crazy- because the pair I bought as a Christmas gift, though pretty, do not have a microphone. Sadly, I will be returning these.