Avery makes these. Item number 75225. I trust that theirs are probably pretty risk free, as far as that goes. Can cheaper versions be made of a material that can cause issues, or is this category of plastics pretty risk free, generally speaking?
I use them on Vario pages. I've never done it, but I'd be nervous using these on unprotected pages with hinged stamps, or even mounts. If you have a cover sheet inside the binder, I guess that wouldn't be a concern.
Just an idea. Check your local library. They continiously throw out older journal books and minutes since the rush to digitization. And many contain page lifters as well as binders themselves. Its economical and recycling all wrapped in one.
Also since they are made of plastic, I wonder if anyone had access to use a 3d printer? And maybe buy a couple spools of material and make your own.