Yes, I typically use FiLMiC. I used it for this video.
However, I would disagree with those who say it works better with FiLMiC than it does with the native camera app. I see no difference whatsoever in my tests.
Not only that, I have read that if you turn off IS in the FiLMiC app that you'll get better results. Even the folks at FiLMiC seem to agree with this because if you turn on the Osmo option in FiLMiC it disables the software IS. However, I find that without the camera's IS active, the results are even worse.
AFAIK, the best results come using the tele lens (the lens without optical image stabilization - the built-in hardware stabilization). The wide lens with the optical image stabilization produces quite horrid judder effects. It doesn't matter whether you're using FiLMiC or the native camera app.
I only use FiLMiC with the Osmo for the higher bitrate options and the other photographic controls/options that it provides.
FiLMiC Pro with IS enabled, tele lens on iPhone 7 Plus
the native camera app, tele lens
using the wide lens with IS on
FiLMiC with the IS turned off, wide lens
Much of what I'm saying is corroborated in this video on my channel - https://youtu.be/ZHdn6RJoss4