I really like this mic adapter. A lot of people are complaining about its bulk but for my use its fine. I like the pass through so I can charge/or add external battery while recording.
I have really enjoyed everything I have bought that is GoPro. Wasn't sure at first but picture, quality, and sound has not let me down yet. Would recommend to anyone looking for a very multifunctional camera. As for the adapter. It works exactly as advertised. Perfect!!!
When this is working, it's fantastic as it allows me to plug in a Rode lav mic for hugely improved audio. So, for at least 75% of the time, it's GREAT. But sometimes it causes (? amplifies?) a weird helicoptering sound. I don't know what it is, and have so far not been able to predict when it will happen.
And yes, it is bulky and a little awkward, but I knew that going in. I can deal with that in exchange for the audio improvements.
Gopro is slowly going downhill. They do not listen to their customers in regards to the user compatibility. This is by far one of the worst designs I have seen. HUGE FAIL!