"However, some may be slow to render (like PDF), so lsix doesn't show them unless you ask specifically."

This kind of arbitrary special case can often be aggravating in software. Something's mysteriously not working for some reason and you have to hunt around to work out how to "fix" it. I'd rather see it being slow on some files (which is understandable) and if it's a pain, look for an option to skip slow files.