I have the John Pearse ebony slimline junior armrest on my Cordoba 55FCE guitar and I love it. So much so that the DeVine classical guitar I have on custom order will come with one as well. Admittedly, I feel comfortable using it on a less expensive guitar like the Cordoba (for any finish damage), and I was not worried on the DeVine because Eric DeVine recommended it himself and I figure he knows what works on his finish.
SCGC koa Firefly, Grimes Hapa nylon, Emerald painted X7, Taylor K24ce, DeVine koa classical, Moore Bettah ukulele, KoAloha KTM-00 ukulele