I always just liked the stereo splitter. No batteries, cheap and it worked, whats the issue.
* Connecting an extra unpowered set of headphones will drop the overall impedance and depending on your source (e.g. a smart phone), you may not be able to get a reasonable volume.
* Related to above, if you have to turn up the volume too high when using two headphones, you can easily damage your hearing when going back to one without lowering the volume.
I have personally been bit by both.
That's what I believe as well. However there is going to be a lot of traditional headphones left on the market.