If you want to use RZ or RB lenses (I have RZ and don't know much about RB lenses) you need to replicate the bellows as the lens doesn't have a focus ring. I have the RZ adapter from Fotodiox for Canon EOS and it works quite well. You turn the barrel of the adapter to focus (replicate the bellows). I have also been looking at RZ/GFX version and it seems quite good. I don't think the kipon unit you have found will work as it is a static adapter and you would not be able to focus to lens.