Picked up some Absolute Black oval rings to see if they make a difference for my dodgy knee. Going on a 1×9 setup.

The info with them says a 10sp chain must be used on a 1×9 setup. I don’t want to doubt their expertise, but this is not something I’ve ever heard of, and I can’t quite get my head round how this might make any difference just because of the wonky chainring design. I thought 9 & 10 speed chains were the same internal width, so how can it make any difference?

Obviously I can just try it, but I’d rather avoid having a ride spoiled by running the “wrong” chain (assuming I can’t tell from a car park spin of course).