I am using one of the Leitax Hong Kong knockoffs myself on a lens that I'm selling, and I've used them on several other R lenses. They work perfectly, but I use mine on Nikon AF film cameras. I assume they work the same on the DSLR's.
I'm not sure the camera's metering is accurate on a manual focus camera because in my experience, as you stop the lens down, the central split prism on the focus screen darkens, throwing off the in camera's meter. It may work right, but when I tried the R lenses on Canon cameras, which use a simpler adapter that doesn't require switching the lens mount, my Canon film cameras didn't meter accurately due to this issue. The Canon's metering software also has a curve built into it, throwing the meter off when you use lenses that aren't Canon, even when you have a chipped adapter. Some of their DSLR's have this issue while other models don't.
On Nikon SLR's, I have found differences in how the camera meters, but haven't had any inaccurate metering. For example, on Nikon N8008s and N6006 SLR's, the cameras will work in A or Program modes w/ stop down metering. This means you can change the lens aperture, and the speeds will scroll up or down in sync w/ aperture changes. You get in viewfinder speed readouts as well. When I tried the same Leica R lens on an N80, this feature didn't work, and all you had was manual metering. Focus is a lot easier on the N8008s and N6006 cameras too because they have brighter viewfinders with higher magnification. The focus confirmation light in the viewfinder worked on all of these. If you have any questions about adapting a particular Leica R lens to a particular Nikon camera I would recommend contacting the Leitax people, as they're the originator of these adapters, and have the most up to date info. I absolutely love using R glass on Nikon cameras. It makes for a much more user friendly setup than on all the Leica R bodies I ever owned.