You missed number 4...
Those who are happy with a bit of card stuck to their monitor - which is less intrusive, or those who have already made their own on-screen ruler, which is free and more customisable than putter pal, and done to the individual's requirement.
I used to use a piece of card, but I'd also created a far better on-screen ruler way before putter pal came out. Still preferred the piece of card for a long time afterwards, but eventually I moved to the on-screen ruler and now use it all the time, except when I'm in "hit it and go run after it and hit it again" mode.