I use my ETRS fully manual, never have got around to getting a metering prism. I do have a "simple" prism finder though - it makes it a lot easier to shoot in portrait mode. And since portraits is what I did with it for several years, it was great.
My 75 and 150mm are "E", the 40mm is "PE". The main difference is that the PE allows setting the aperture at half stops - in manual mode too. I actally bought th 40mm new, since the price difference (at that time) between new and used was so small that I decided a new lens was worth the little extra. All the lenses are excellent.