Great shots! But be aware of side effects of CPL

Here is one of my photos showing side effect of CPL+wide angle lens. Apparently it's darker near center and lighter near the edge. I used to have CPL always on my 24-105 lens also as a protective filter in addition to filtering the polarized light. I no longer do so because of this side effect. The other side effect is that the outside border between sky and any objects such as trees appears brighter (noticeable in your picture 6). I also have a few examples of that edge effect.