Beautiful, original idea, but a bit too easy. At first sight it looked like a devil of a crossword, but after ten minutes I knew it would be a quick solve. Still, as I said, a beautiful idea
I can't parse 1 either, or 21. All done, I agree that it may have been a bit too easy maybe. After the past couple of toughies, I suppose a weekend free for other pastimes will be welcome though.
I thought 1 was pretty easy to parse once I'd changed one letter from my original assumption. I have done almost all of the clues but haven't had the PDM about the theme! Worried it may be one of those areas of human endeavour that is Simply Beyond My Ken...
I'm unfamiliar with the subject matter so struggled to justify 15 despite having all 6 letters by the end but found that it is listed in Collins if not my version of Chambers.