I have the acute matte SI-grids in two of my three bodies, I prize them for landscape and aerial work. The image will be much brighter, feels like a new camera. The split is very handy for low light, fast focusing and tired or wind teared eyes and can be oriented either horizontal or vertical if working predominately in either. The grid is pretty handy for landscape, aerials or architecture but can be a little distracting for subjects like portraits, candids etc.
One particular topic I find the grid invaluable for is memorizing double or triple exposure placements. For example, (there was a url link here which no longer exists) I am working on requires me to have precise placements of components in the frame, the grid is KING for this....