I have one of these for cellphone use only. A single earbud, and no A2DP stereo profile. For me it is great. I don't have the geek look that allows me to where a BT headset throughout the day, nor do I want to. So, this setup works very well. Plus I hate having things stuck in my ear for very long. I can clip it to my shirt, and hang the earbud on it, then when the phone rings I just grab the bud and stick it in my ear. It is very handy, and it was cheap. It is not awkward with the short wire and it isn't connected to something else to cause a hassle in handling it.
I think the idea behind this for stereo use is for all those people who don't like headphones, and prefer earbuds. This works very well for that purpose.
I'm just guessing but I'll bet that the second bud being able to unplug is so you can use it with a single bud with a cellphone. I would imagine that the second bud only has one channel, so plugging headphones into it wouldn't work very well.
Dave