as far as anyone knows, f2 and f3 differ only in what paint colors were originally offered
yup you got it pretty much right... fastfromthepast sells Tarozzi, who offers both complete bolt on rearsets for specific applications no additional parts needed
or...
universal rearsets including just pegs, levers, and linkages and you must figure out how to attach them to your bike
...so Cognito is just using the universal set to which they add there own mounting bracket, and to be honest, the cb550 brackets I have from them are ridiculously overbuilt, heavy, and crudely torch cut from 1/2" steel plate. I think these have been improved since then at least as much as they are available in aluminum, but not really sure
Overall, the quality of Tarrozi stuff is not stellar either, especially given the price, the castings and finishes are somewhat crude. But the stuff fits and functions, is very well designed, holds up better than it looks like it would, and fastfromthepast offers every single little nut, bolt, clevis and casting for replacement if you break anything.
I have Tarrozi rearsets on 2 bikes, one for a few years, and 10s of thousands of miles and am well pleased and will certainly buy more. I have also pieced together rearsets from some of this and a little bit of that, and I can tell you, it is very time consuming and the results were less than satisfactory. So maybe buying the specific fit application is not such a bad deal after all.