I finished Kump's book, though not all the exercises, and find myself satisfied with the improvement in my reading speed.
The only technique I ever use from the book is that of 'setting intentions' before I start to read, which often helps me feel good about skimming something very fast (as opposed to feeling vaguely guilty about how fast I'm going, or, worse, slowing down to take too many notes) when I'm trying to get the gist of something. I also think my fast skimming might be slightly faster from the practice, though I haven't timed myself.
I think I would have found the techniques more useful if I read books on paper -- some of the full-page gestures were indeed very helpful when I tried them on a paper book acquired for the purpose. But, I hate reading on paper, so that wasn't as useful as it could have been.
I've been getting slightly more use out using Spritz in the iOS app "ReadMe!", though I don't know yet if I will have patience with its poor UI (and attempts to make me spend money) in the long term. I also doubt it would be useful for anyone who wants to read contemporary fiction, since it doesn't look like it plays nicely with purchased eBooks. All I want to do is read 18thC novels in astonishing bulk for my dissertation, though, so Spritz/ReadMe! works great to plow through the ones in Project Gutenberg.
Overall, I'm glad I read Kump's book, and glad that halfway through I gave myself permission not to stick too closely to the exercises and just read it lightly for general information. I'd recommend giving it a try to anyone who wants to think through their reading habits and how to make them faster, and particularly to people who need to get through a lot of physical paper pagers.