@ the :02 mark at the start of the video the stock lens on the lower left is shown compared to the 3.97MM lens on the upper right. Notice how the 3.97MM lens reflects the light and appears clear in appearence where its front element meets its mount. The stock lens front element to mount seat is blackened for a very good reason.
I personally would not pay $140 dollars for a lens that can be sourced for less than $50 dollars. When selecting any lens,one must take into consideration how that lens handles light and addresses chromatic abberations. Though I applaud the efforts of the posters of the lens replacement video,I also understand you do not have to strip the camera down that far to replace the lens.
Depth of the front element means nothing. The lens that they used is very much an upgrade from the crappy lens that Yuneec is using. and if you can source the same lens for $50 I'd love to see where you get it. the $50 versions I have seen don't resolve enough line pairs for the 12mpix resolution of the camera. I've seen the $50 ones and they are suitable for 6mpix cameras
What are you referring to when you state "Depth of The Front Element Means Nothing" ? Just because you cannot find a 16 megapixel replacement lens for the pricing I mentioned does not make it so. I know better. Having both a 3.87MM 16 megapixel and 4.35MM 16 megapixel lens fully tested on a GoPro Hero4 says otherwise. Both lens are glass,multi coated, IR cut rear filter and metal in construction. One costs $39.00 and the other $49.00. If you care to visit my blog over on RCG you can see the results of my tests of one of those lenses.
Many of us want a lens with a narrower field of view than that provided by a 3.97MM lens. It is both doable and affordable!