Greetings. I'm new to the forum and immediately gravitated toward this thread. The first time I found this forum was when I went looking for opinions on guitar supports and there are many! I have to preface any comments by saying that I'm a beginner, but a zealous one. I practice a lot right now, and I can feel the effects of it on hips and back when I get up. It was causing me some asymmetric strains that I started to notice while at work, standing up, and I do tend to get some low back discomfort if I'm not mindful of my posture, so I decided to experiment with supports.
I tried a number of supports including the cushion and often felt like they moved the guitar away from the spot I expected to hold it, maybe not much but I noticed. If I had gone with the cushion, I would have ended up modifying it.
I ended up liking the Tenuto rest, which is a kickstand type like Gitano and others. I do have a very level guitar seat, which is a keyboard bench and I agree that level thighs help a lot. I've played on other seats and had to readjust for thigh slide.
I have this idea for throwing a rare earth magnet in my pocket and pinning another onto the guitar support strap material where it sits on my thigh to see if that gives it enough *stick* to fix it in place. This is one of the modifications I would have considered for the cushion as well. However, with a level seating posture it's not a priority.
I do think the support has allowed me to go for much longer practice sessions without a tendency to have one-sided back and hip stiffness.
The soreness is now much more uniform and symmetric!
"If I have seen further it is by standing on the shoulders of giants." -Sir Isaac Newton
Armin Hanika 56PF