YT addons generally don’t work on Piped, but some of the most popular ones are already built in, like SponsorBlock, DeArrow and Dislike. It does show comments, but you can’t post any comments yourself. HDR videos should work since it’s just pulling the video files directly from YT servers.
You can just try it out, simply replace “www.youtube.com” with “piped.video” in any YT video or channel url.