I have been using the Murata guitar rest (one without suction cups) and it certainly makes me play much longer without any backpain. I even saw Goran Sollscher using it on a concert stage a couple months ago. The guitar rest stays intact without making any squeaking noises.
But I realized one problem. When it is tight enough, there is noticeable loss of tone (and maybe little bit of volume too). Has anyone noticed similar problems?
These days I wound the clamps with soft clothes. The tonal loss is minimized but it is still a bit slippery.