Honestly, it's painful to play hunched over at this point in my life.  The A-frame allows me to sit up comfortably like I'm wearing a strap , but without the added weight on my shoulder.  It's pretty easily adjustable.  I find myself using it on either leg (classical style or traditional) and it works either way pretty well, keeping me from bending.  In the past, I've had one of the cushion-style supports and they just aren't the same.  You can't adjust them well enough to really use them to suit your specific needs, depending on your height, guitar etc.