I don't think the highlights are bad here. It would likely be better to reduce them in camera rather than having to do it in post, but I don't think you've got a bad result at all. The key is shiny so I would expect to see highlights.
The problem with using a circular polariser is you will significantly reduce light hitting the sensor (something you want to specifically avoid with macro). Furthermore the polariser is dependent on directional light. In most cases you want to achieve soft, diffuse light (i.e non-directional) so the two aren't really compatible. I did see some theoretical designs for a diffuser that gave out directional light, specifically to work with a CPL in macro situations, but whether or not it worked, or even saw the light of day, I have no idea...
I prefer the first over the second as the light hits the subject better and makes it pop more.