Update: I was able to ride the course in Winter Park that my wife was racing on (I can’t race yet after surgery). I was using 1 1/2" back rod inserts with a Ikon 2.35 up front and an Ardent Race 2.25 rear. Running 21R / 16F. Course had sections of roots, round and square edged rocks and also some loose descents with 4-6 inch rocks rolling around. I ran 2 psi less than I normally would on this course with those tire sizes and I definitely could tell the difference.
I felt like I had 1/2" more suspension with the lower pressure and more grip, but the tire never got close to dinging the rim when I went over a sharp edged root or rock. It felt like you get the grip of having more tire on the ground but you get better fold over and snake bite resistance. As the tire deforms closer to the rim it is supported by the insert and acts to increase the ramp rate. I really liken it to adding tokens to your fork. You can run lower pressure to get better small bump compliance but as your go deeper in the tire travel you get progressively more resistance to bottom out.
It also gives you support when climbing seated and you go over a root or a rock. Almost as if it is pushing you up and over it. I think this is because the tire isn’t conforming as much to the rock or root and getting stuck on it as you pedal over.
Anyway that was my first true ride on it and I’m sold at this point on the idea. I didn’t notice any rolling resistance difference in the flat or fire road sections and there was a section of this trail that is flat’ish, fast, and had roots across the trail. I was able to stay seated even more than normal on my Scott Spark and just motor through these sections without as much unweighting of the saddle when I came to a rooty section.
your mileage may very depending on that way you ride. If you’re bashing your way through everything you might need to go with a heavier duty insert like a Huck Norris or Cushcore. But for my I ride lighter on the bike so it works great for me.