I use it and it's quite effective. I just paste text I want to summarise and just ask (GPT-4) to "Create Anki cards for these paragraphs. Keep the answers brief". It does quite a good job in distilling the knowledge.

And for cards creation in general, the ever-green "20 rules of formulating knowledge in learning" is always a good guide.

http://super-memory.com/articles/20rules.htm

I haven't tried it. But it's a two step process:

1. Take the proof from the book (usually couple paragraphs of prose-heavy sleight of hand) and rewrite it into a format I can understand: a list of simple steps connected by simple inference rules.

2. Split them up until each proof is 5-7 steps.

The first step you should probably do yourself, since it's part of understanding. The second step GPT can probably help with.