I have a PM6 domed lens and it's nothing more than that, a dome shaped lens as opposed to flat. It does not change the beam in anyway as far as I know or can tell.
I have it installed on a BA McLuxPR head and sometimes I forget it's there. It's way more noticeable when I stick it in my black PM6.
I like it cause it's different, gives the light a different look. I don't have one installed on my EDC McLuxPR though. Is it worth the extra money? Probably not but I'm still got some on my to buy list.
I have a couple E2es and had no idea that they had domed lenses. Mine are flat on the outside so I assume the inside surface of the lens is where it is domed? If yes, the domed lenses from the shoppe are not like this, they are curved on both sides.