O.K. Michael, I'll take your cue.

I started using armrests on my Grand Concerts. I was skeptical after reading posts about them, but tried the test that folks recommend - play as you normally do, then play again making sure that your forearm does NOT touch the soundboard. For some folks it makes no difference, but for me I noticed that my forearm was damping the guitar slightly. This can be especially true on smaller-body guitars like the Grand Concerts. So I tried a John Pearse armrest. It keeps my forearm off of the guitar top so there is no damping.
I was not totally satisfied with the fit and finish of the purchased arm rest, so I cut it to a smaller size and shape and refinished it. In the process I also made the edge radius, where your arm touches it, larger and more comfortable.
I've since made more for other guitars. I like the large edge radius so much that I put one on my Grand Auditorium as well, even though the "damping test" did not show that I needed it.
I'm a big fan, but I know they're not for everyone. As I said, I really like the large edge radius, but the one downside is that the rest effectively makes the guitar about 1/4 inch deeper, so you either have to put your playing arm out farther, or tilt the guitar back toward you.