Just received and tried this mic. Some thoughts:

Well packaged, but there was no battery in my box even though it states on the box that the battery is included. Not a huge deal, and I'm sure it was a one-off fluke.

I just compared it with the Sennheiser G3 wireless system with an ME2 omni mic.

The Boya is more Midrange forward, with less clear high end (air) and less fullness in the lows as well. Interestingly, noise is very well controlled. As a matter of fact, I'm really impressed with noise levels. The noise that I do hear is what is more or less always present when recording direct to the GH3 mic input.

After EQ-ing the Boya, I was able to get it to sit very well beside the ME2 recording. However, this did highlight the noise a bit as well.

Overall, very well worth it for someone that needs a very inexpensive but totally usable wired lav mic. My recommendation: Beginners should by at least two, and pros should do the same. In the case of the latter, this would make a great mic to have in the bag as a backup if a wireless setup fails, or perhaps in a situation where the conditions are rough enough to warrant using something that is more or less disposable (based on price, not quality).

Build quality seems perfectly fine.