There is a notice on this wiki that contains some comparisons: https://thewiki.moe/guides/playback/

I'm sure you can find some more in-depth explanations but I will just copy/paste a quote I have seen from reddit.

• uses wrong matrix for RGB conversion (results in wrong colors)
• uses point upscaling for chroma planes
• introduces strong banding
• wrong chroma location (MPEG-1 for everything)
• Old subtitle renderer that in more Typesetting heavy situation will say fuck you
• all the other bugs (including some that haven't been fixed in years) make it equally unsuitable media player.