I see alot of people saying they won't work with Ego batteries which is true but why would you want to test a Ego battery with a screw on meter? It's regulated and we already know what the voltage is.
These are handy for variable volt mods that don't already have a meter and testing under load, which they do well. You can use a multimeter on a Ego battery if you really want to verify it's under 3.7v.