I just use one coat of FK.
It's more down to the preparation and application than anything else.
When i clean the wheels i completely strip any existing layer of by cleaning with Bilberry wheel cleaner, Tardis, Iron-X and washing up liquid. I then IPA the wheel down twice and ensure it is bone dry. Then and only then do i apply the FK and let it cure for at least 30mins before buffing off.
The main thing that attracts me to FK is that it is a similar price to C5, seems to last just as well and i would literally 1000's of applications from one tin vs 4 - 6 wheels worth from one 30ml bottle of C5.
As said though i will do a direct side by side comparison when i next clean my car around July/Aug time.