My favorite feature of these earphones is the high noise isolation and relatively accurate sound reproduction. Etymotic Research also offers the more expensive ER4 earphones, which presumably sound quite a bit better ($350 vs $65). I like the mk5s for running and general listening. They are easy to drive from a smartphone or laptop. At $65, if they get lost or stolen not that big of a deal. I've had mine for over 3 years and they're still going strong.