Last year I bought one of the 44" Project X (red X) wood shafts, made for some OEM, that were all over the web for $15-20. I reshafted it into a 4 wood that I liked. The PX had the right weight, torque, and butt CPM that I wanted, but the club turned out to be unhit-able. I mean it was bad.
I just figured it was not a good match for my swing, so I pulled it and put it in my "inventory". This week I was scrounging for an appropriate shaft for the 9 wood head I had, and decided to look at that one again. I put it in the frequency meter clamp, and when I twanged it, it had a huge wobble. I am pretty sure I didn't bother flo-ing it the first time. In the past few years, shafts have seemed to be quite good on that score. So anyway, I started finding the FLO on it. At the worst point, the shaft was wobbling almost side to side when it was supposed to be going up and down. Maybe the worst I've ever seen, or at least top three.
I did find a stable orientation, where it could be twanged either vertically or horizontally and would track like it was on rails. I think this is one of what we used to call "type 2" shafts, which have two spines 180 degrees apart. Supposedly if you orient them at 6 and 12, the shaft would be a great performer. Anyway I put it into the 9 wood, and it plays great.
So when someone tells you spine and FLO don't matter, they are probably right, except when they aren't!
I sure would not have wanted to use this shaft in an adjustable club.