I have an r3a, and I know damion and skorj use one too. I absolutely love mine and it is a dream to use. The r3a does have a 1:1 finder which is ok - I'm not too keen on it for the 40mm lens I have (it has framelines for 40 and 90, 50 and 75),as the frame lines are right on the periphery and sometimes difficult to see. You really can use it with both eyes open and get a kind of frameline superimposed on your normal vision, cyborg-like.
I really like the aperture priorty mode and only use it in this, that said, a couple of times, i've forgotten to turn it off and drained the batteries which is a pain. Thinking back on it, I'd probably have gone for the r3m if it was available at the time I bought it.
I only have a 21 wide and 40 for it, but I'm keen to get a 75mm one day which I think would make me use it more.