I have not personally used one, but my buddy has one and we often compare video quality vs my GoPro (at the range, so all things being equal). the GoPro produces much higher quality picture and sound. While the GoPro is more expensive and the mounts are not as elegant, I make it work.
I am tempted to try a tactacam at the price point and eventually I will. If you do not have any other video means, I would not hesitate to buy/try one even with my limited exposure to them