The thing I love about these ND filters is the quality of the glass and the housing. I have noticed very little if any color shift and zero vignetting. The latter has more to do with the design of the GoPro lens, than it does with the design of the ND filter. The filters came quickly and were packed well with no damage.
I use the ND32 filter the most on very sunny days in Southern California and utilizing the 180 degree shutter rule, I am able to achieve an acceptable exposure. I still have to reduce the brightness about a 1/3 to 1/2 stop to get perfect exposure in post editing but that’s not a big deal for me as I like to color correct all my footage anyway. Perhaps an ND64 would be perfect. For the quality and performance to price ratio, I highly recommend these ND filters.