I play a mixture of styles, mostly flamenco and Brazilian music, as well as some classical. Anybody playing a classical or flamenco guitar has at some point considered using a footstool to get a comfortable playing position. Flamenco players tend to be less formal, and often simply hold the guitar on their lap in a cross-legged position.
Whereas the classical-style position using a footstool produces a pretty good ergonomic position for the arms, I’ve generally opted for the informal flamenco position. My hands are pretty strong and flexible, so I can actually do pretty well either way. However, I’ve done really long solo gigs, and these can be tiring. In those cases, I would switch from one position to the other every so often, and that was helpful.
I’ve always been a little resistant to the traditional classical position. For one thing, I don’t like carrying a footstool. I also am not especially classical in my mindset. 
Finally, though the footstool position is pretty good for the hands, I still find the footstool method to be uncomfortable for long periods of time.
Enter the Ergoplay Support. This attaches to your guitar with suction cups, and it becomes a guitar rest that sits on your leg. The beauty of it is that you get the hand benefits of the classical position, but both your feet are on the floor, so it’s better for your back, and back fatigue was what made the footstool position annoying for me.
I’ve had mine for a couple weeks now, and I love it. I can even use it while sitting on the floor. Things are just easier to reach, and I don’t get tired as fast now. The playing position is good for either hand, and my technique has suddenly gotten a big boost. When the hands are happy, the music comes through more easily. And playing tricky classical material, like Jesu, does often work better playing in this position.
When using the informal position, I have an old habit of staring at my left hand while playing, and my head tilts and turns toward the guitar neck. With the support, I tend to avoid this old habit more, and often don’t look at the neck much at all. There are two benefits to this – one is that your neck doesn’t get tired being in that funny position, and besides, I find that when not looking at the guitar, I can concentrate more on the sound and feeling of the music, and that’s been very exciting.
The only downside I’m aware of is that if you have a matte finish on your guitar, or a fancy French polish, the Ergoplay’s suction cups could do a number on it. Ergoplay includes material that you can stick on the matte finish, and then you attach the suction cups to that material instead. But I’ve read that some fancy and finicky guitars don’t like that stuff either. But if you have a glossy nitro finish, you should be OK.