From that post in the thread, AI and placement start to be the suject of the discussion.
https://forums.online-go.com/t/handicap-etiquette/17218/31
(Thx @Vsotvep for the link)
To resume
In term of points difference between free and fixed, that’s nothing so important but some free can be much worse
In term of usefulness, more should be considered as only the points value, like solidity, easyness to handle, fitting the play style, etc…