I use it on mobile. Still better than the new site. Chrome has bugs with the "text scaling" feature but if you turn it off then old.reddit.com works fine.

Like the sibling commenter, I use old.reddit.com on mobile - but the key being that I switch the browser into Desktop mode.

In posts with embedded pictures, I have to remove the "old." in the URL in order to be able to see the pictures, switching to desktop mode doesn't solve the problem.