Years ago I got some for the 71 when I was ordering up a bunch of brake parts for it anyway. They work ok, but you have to ensure the threads don't leak. They got some sort of sealer on them to prevent that from happening, but not sure how many times you can bleed the brakes before that wears off.
But I had no problem being able to bleed the brakes by myself and they did work. So...there's that. Would I get them again? I doubt it.
Put that 20 bucks with another 20 bucks and invest in a good mightyvac hand-held one-man bleeder kit and you can do it mostly under the car for all your vehicles. With the mightyvac, any air leaks that get around the bleeder screw would get sucked right out anyway.