Another guitarist b***hing about your strings IS a good indicator. However I recently lent a guitar of mine to someone during a song circle , who chose that moment to chide me, to my chagrin, within the entire circle about the state of my strings.   Words failed me, but right now, something about not looking a gift horse in the mouth or biting the hand,etc. or such is my 20/20 hindsight comment.

PLEASE if someone is gracious enough to lend you a guitar, make your observations in private - or your donor will not be so generous again.

I AM going to try those John Pearse next, heard good things about them.