So far, once I figured out that they wouldn't work on CR2/ORF/RAW or other raw files, I exported image as a JPG. So far, I have gotten good results with Nik Viveza 2, Define 2, Color Efex Pro 4, HDR Efex Pro 2, Silver Efex Pro 2, Topaz Labs, and Focus Magic. Alien Skin plugins have issues with Pixel transparency, Piccure and Piccure Plus just don't start, and neither do Redfield plugins.
Now I know that many of these haven't been tested by Affinity programmers, but I thought I would give them a try.
Overall, I am rather impressed.