I like the KLEI binding posts and have used them for several amplifier and speaker projects. They are nicely made and easy to work with. The low mass design is consistent with Allen Wright’s ideas in his SuperCables CookBook which I find effective.
The Naked Harmony conductors are unplated which can make a good connection, but surfaces will tarnish over time and require periodic cleaning. The Classic Harmony conductors are gold plated to maintain a good connection without cleaning. Otherwise, the two models should work and sound pretty much the same.
The Naked might be better for a copper-to-copper connection? Classic for other plated connectors? Just a guess.
WBT makes similar low mass binding posts but I have never tried because they are considerably more expensive. Of course, WBT has a good reputation for quality and workmanship.
I don’t know if anyone has done a head-to-head "shootout" of binding posts to evaluate their impact on fidelity. It would be a challenge to do and I imagine differences would be subtle.