When connected to an Axiom 7" DVD player (http://amzn.com/B003YXZNOI), connecting 1-2 sets of headphones, sound quality was similar. However adding a 3rd set did cause volume to get quieter (expected, Ohm's law, whatnot). The rigid design, however, required the use of an extension cable from the player because the adapter wouldn't fit within the case we were using. This wouldn't be a limitation with adapters which use flexible cables.
Despite this, it did the job for the intended role, and made it so that 3 kids could enjoy movies from a portable player without driving their parents crazy on a road-trip!