For "heavy duty" lapping work, I use 3M sandblaster paper on my counter top, as I mentioned here. I use it because it's readily available, works well, and is inexpensive.

Other than that I use the DMT 325 (D8C) for regular lapping because it's pretty cheap, fast, easy, and convenient to use.

I don't own enough hones or razors to invest a lot of money into lapping with the DGLP, and I really can't imagine that the extra flatness would make any real difference in my shaves