No claims on brightness either way there Jake. Having run both theirs and ours side by side I can personally vouch that they both hurt to look at!
Follow the Suntail instructions, which would essentially be to wire it directly to your panel switches, ignoring the Flyleds controller.
The Flyleds Kit tail light will flash in sequence with the wingtip strobes, whereas the Suntail will strobe away to it's own tune, so to speak.
The Flyleds Stand Alone tail light flashes out various patterns that would also be out of sync with the wingtips.