I have an RS40 and have been using the ZOOM method for 2.35 ( I don't yet have a screen just a 14' wide beige wall ). I recently bought the UH480 used as a "C" stock item on VideoGon. I grabbed it because I wanted to play with it, and at the price, I knew I could sell it with minimal loss. My set up is sitting on a table, and I've not messed with it too much other than to get the picture to shoot through the lens onto the wall with no light loss, maybe 5 minutes of set up.
The difference between zooming 2.35 and using the anamorphic mode with the lens is night and day to me. I think you are loosing like 5% or something like that of brightness, which in a light controlled room is negligible, and even with the lights on is not really noticeable to me. So the picture quality and sizeing options that open up with the lens outweigh any light loss for me.
I plan on keeping the lens, I'm happy with it. I haven't decided if I'm going to sled it or just use anamorph B mode on the proj and just leave it in place.