The only issue that I noticed is that Mac desktop old Mail App doesn't show HTML images at all.
I tried the following set up (mail -> preference -> viewing -> Display remote images in HTML message) but still didn't fix the problem. It's no big deal to me but if you have a solution, it would be great to know.
Some really nice designs - just a quick note. I am using Windows 10 and viewing the above in Edge and Firefox. Firefox they are looking as expected - Edge is a mess with the generated code on the emails above. Gaps, missing colors, etc. Just something to be on the lookout for.