>Do the 3rd party providers guarantee perfect compatibility and >warranty against any issues with the camera that may result >from the use of their products?
Perhaps not. I purchased my Nikon genuine article for the same reasons you did. I just haven't heard any complaints about the performance of third parties here or on other sites. Metal is nice, but plastic can be very tough. My D70 wore like a tank until I passed it on to a relative who is still using it. It has been all over the planet without even the hint of a crack or chip.
Frankly, I hate the design of the multi-selector switch on the Nikon MB-D11. I find it very difficult to use and it is disappointing that so many third parties have so faithfully copied the Nikon design If I was in the market for another, I'd give Pixel's a try. They've made a change to the form of the grip around the multi-selector and to the multi-selector itself that looks like it would address my issues with the selector.