It's a lossless format optimized for file size rather than decompression speed; the README seems clear enough. Made by a pixel art game dev, for compressing sprites in pixel art games, so I assume it fits a useful niche.
I don't see any hassle, really. It's just another image format: good for some use cases, bad for others. No one file format is perfect. It was interesting enough for me to give it a couple of hours to implement a cli and add support to my pixel app.
https://nigeltao.github.io/blog/2021/fastest-safest-png-deco...
PNG decoding seems to be fast enough:
Anyway, PEP is interesting!