Hi shifty1981,
Post #2 here includes my thoughts about the pros and cons of split layering. If the cover and quilting is suitable for “split layering” on the top layer or there is a top layer of foam on top of a split layer then most people wouldn’t feel the actual split itself but of course there would be a noticeable difference in each side of the mattress and for those who use the middle of their mattress more than others this difference in firmness and how far you may sink in to each side (which is the reason for the split layering in the first place) would be more noticeable. The bigger the difference between the two sides the more noticeable it would be and this may affect some people or couples more than others. There is also more about different ways to accommodate the needs and preferences of a couple who are very different in post #2 here.
Phoenix