My warning about the feature differences was meant to temper ag users' expectations. There are lots of little things that ag users are accustomed to that are either different or missing in ripgrep. Off the top of my head: Ag reads the user's global gitignore. (This is harder than most people think.) It detects stdout redirects such as "ag blah > output.txt" and ignores output.txt. It can search gz and xz files. It defaults to smart-case searching. It can limit a search to one hardware device (--one-device), avoiding slow reads on network mounts. And as a commenter already pointed out, it supports the --pager option. Taken together, all those small differences are likely to cause an average ag user some grief. I wanted to manage expectations so that users wouldn't create annoying "issues" (really, feature requests) on your GitHub repo. Sorry if that came off the wrong way.
On a completely unrelated note: I see ripgrep supports .rgignore files, similar to how ag supports .agignore. It'd be nice if we could combine forces and choose a single filename for this purpose. That way when the next search tool comes along, it can use the same thing instead of .zzignore or whatever. It would also make it easier for users to switch between our tools. I'd suggest a generic name like ".ignore" or ".ignores", but I'm sure some tool creates such files or directories already.
Edit: Actually, it looks like .ignore can work. The only examples I've found of .ignore files are actual files containing ignore patterns.