A couple of additional points to consider.
First, Rockler sells hardware that will grip inside the miter track, so horizontal feather boards can be used with the miter track. But, the grip isn't as solid as that using T-track. Thus, having a T-track parallel to the miter track might be useful.
For fence-mounted vertical feather boards, the design of the feather board becomes critical, particularly with relatively short fences. If the "minimum" position of the mounting bolt slots are too far above the tips of the feathers/fingers, the feather board becomes useless for all but the thinnest of stock. (As you might guess, I made a couple of feather boards without thinking about that issue.