I have a Maxwell with the grid, and no split image. I see no need for the split image, and think it would more of a distraction than a help. The snap of the focus is quite effective with the screen alone.
For awhile I had the same screen without the grid, and it was my favorite, especially for portraiture. The grid lines are handy, however.
I haven't seen a screen with the crop lines, but it sounds useful if it is not too distracting for normal full-frame use.
I do find the crop lines on my Mamiya RB67 screen distracting, but don't feel the same way about the grid lines on the Maxwell.