Even if every earpiece got his own strong feature and consequently no one covers all options possible, there are a lot things in common which allow us to compare the market and seperate the hearables from the headphones or headsets.
Besides battery life, recharging cycles of the transport case is one key to consumers satisfaction. Audio transparency as a safety feature is as irreplaceable as a full hands free use (except the corresponding app) for the comfort and the feel of your new inear buddy.
If I want fitness tracking on board, I need a waterproof surface, or at least splashproof. Internal memory is nice to have, especially if you are not a 24/7 smartphone addicted user, but it is less important then the question, if your new hightech gadget can go with iOS and/or/but not/only on sundays with Android.