I never intentionally used any AI features in Chrome but first was made aware of the models when my disk was running out of space. I investigated with a disk usage tool and found I had multiple versions of the model in my Chrome directory taking up ~12gb. This was about half a year ago and maybe I was in a bad experiment or something but it's definitely not opt in or user visible. Less tech savvy people will have a really hard time understanding why their disk space is running low.