I use flat fall for everything, YT, rockfish, lingcod. It works really well for me, In fact I have more faith with my jig than live bait. BUT, I'm not using the shimano flat fall. Shimano's flat fall was one of the first generations of flat fall jigs, it's rarely seen now in japan because the newer ones works so much better. Try some "Seafloor control" flat fall jigs, especially the "Rector", I caught almost anything with that jig.
Lingcod is especially attracted to it. You don't need to cast, just drop it vertically to the bottom, depent on what you are try to catch, for rock fish and lingcod, just do slow up lift near the bottom and then drop back, repeat. For YT, do punchy fast up lifts continuesly to the surface with some random drops.
oh, you also need a "slow pitch jigging" rod, those rods are skinny with bouncy tips, the jig will dance better and be more attractive.
I just bought my first kayak, I think pretty soon I will be slow jigging on a kayak, maybe I'll try county line or LJ first.