I have a SR pad and I like mine very much. I was initially intrigued but then turned off by the website. I found the exact one I wanted in near new condition on ebay and bought it for $150.
They are very very well made, take serious abuse, and are worth the price tag from a construction pov.
The pad is a little hard to describe: a leather envelope filled with a few thin layers of materials. The pad is firm, not squishy, but not hard either. Its shaped for curvature of the back. It does conform slightly. Its less than a half inch thick. It does not compress or bottom out at all.
One of the reasons the pad works is because its thick and firm, it distributes pinpoint pressure over a wider area by its firmness. Imagine you are wearing a heavy backpack on a long hike. The backpack doesn’t fit you quite well, slides around a bit and has some pressure points where the buckles are, they dig into your shoulder blades. Now, imagine putting a thick felt/poly/leather pad between your back and the pad. The buckles can no longer dig into you, their pressure is going to be spread out over a larger surface area. With a gel pad, or foam, or even sheepskin or thinline, you can still feel a pressure point poking through because those materials bottom out or are too thin to really block pressure. You can experiment by putting your hand under a pad and then trying to gouge it with a hoofpick though the pad. You cannot feel a point of pressure at all through a SR pad, at least not what I’ve found with my own strength, I haven’t had a shod horse in borium stand on my hand though… however I do recall some youtube video to the extend of something like that iirc?
The other neat thing the pad does that few others do is reduce friction. The horse’s back is a surface that is constantly in motion, we as riders are a living being that are also constantly in motion, sometimes with the horse, sometimes not so much :lol: In between the two of us we stick a large solid object that does not move or yield. That causes friction. If you’ve ever worn full seat breeches on a sticky saddle and the seat stuck to the seat while you slid around inside of the breeches, thats kind of the idea.
The SR pad is made of layers of material for a reason, the layers slip slightly against each other absorbing motion and reducing friction.
There is a reason the US military chose folded wool blankets as the saddle pad of choice to put under their mcclellans 
and its not just because of the double duty the blanket offered.
The SR pad does a lot of great things but isn’t a cure all of course. It won’t stop a saddle from rocking or bridging, it doesn’t fill in gaps or hollows, it won’t level a saddle, and its useless if the saddle is too narrow to begin with. It is ideal however for a saddle that is a decent fit but maybe has hard or lumpy panels (or a western saddle that really needs the sheepskin replaced), or a saddle that is one size too large. I found it worked great on my sensitive backed horse, and I really enjoyed it under my treeless, it won’t collapse or bottom out under pressure at all.
Like all pads, I find it fantastic for certain situations. It is definitely going to stay in my bag of tricks.
Hope this is helpful.
It should be here soon and im very excited to try it on my horses!