It's just horrible. For me the preview doesn't show until I've hovered for ~3 seconds (even before I turned on AI), in which time I could have long since middle clicked the page, skimmed, and closed it again.
This is the content for the preview:
> www.mozilla.org
> What's new with Firefox 142
> What's New | Firefox 142
> 3-4 mins reading time
No OpenGraph descriptions are good, so I can't see it ever being better than this. I don't know why this reading time metric has become a thing, it's useless because it doesn't know which parts of the page I'm interested in. I could actually see the full url from the immediate link preview, so having only the domain here is worse than useless.
The AI summary is both too short and too slow to be useful (unless maybe you're running an RTX 6000 or whatever). For this link, it only mentions Relay.
And even the basic behaviour seems broken. The preview appears at seemingly random locations on the page, sometimes under the cursor and sometimes far below. When it does decide to appear away from the cursor, releasing the mouse button actually follows the link, completely negating the purpose of the preview!