Singh-Ray (Darryl Benson) Reverse ND Grad Filter

I live on the east coast, so I have some experience with Soft Grad ND, but we seldom have a nice flat horizon, so I have never played with hard Grad ND and never even considered a reverse ND Filter (http://www.singh-ray.com/reversegrads.h​tml).
I am going to northern Arizona and southern Utah in August and was considering the latter. Any specific advice, experience with this filter or feedback?

In Africa last year, sunsets with animals below the horizon were a challenge (that was mostly shooting a 100-400 at 400 supported on beanbag in car window, so I don't know I didn't even consider my P size Grad ND, but it seems the 4x6 size could have worked and I like the idea of the reverse ND Grad Filter. Do you think I could have used it in this setting? I will be going back next year.

To me the idea behind a reverse ND is very interesting. I don't have one but is seems that it would do a better job than a standard ND at sunsets. I even wonder why a reverse ND is not a standard and the standard is not the reverse.

However, it is almost impossible to get a flat horizon out west. With a very few exceptions you will always have mountains on the horizon. Often times I end up just taking a few exposures and blending them in PS.

I have one on order, as I like shooting sunrises and sunsets and find a reverse GND would be more suitable for my shots, where the sun is near the horizon.

I would imagine they'd work just like any other GND though. No good if you don't have a flat horizon.

I read on the Singh Ray blog that if you were going to buy a Reverse ND grad, they recommend the 3 stop one.