I have a few of these things, but I'm not a fan. They just don't work for me at all.
I have read that one's eyes adjust quickly so you must use it briefly to see the scene and then take it away or it is not effective. I have read a few posts on photo.net, largeformatphotography.info, and here on APUG that some people like them and some like yourself said they were not useful. Basically why I wanted to try a cheap one, just I was one of those people that did not find it useful.