I've used one for years and never had anyone seem to notice or comment. With all of the accessories and external pockets on most packs I think someone would have to know what one is to suspect the contents. I've also used it strapped to the frame of my mountain bike and it worked well.
I had an occasion to draw from it once on account of a neighboring pitbull that charged my wife and I while walking our dog one morning. The pouch worked absolutely as designed and I don't think an external holster would have bought more than an additional second of time (the pit bull changed his mind at the last minute and veered away from us).
