FYI I have the Borg 55FL which has even more FC. I fitted it recently with a TS flattener and now I don't have to refocus to see nice stars center or edge. This model flattener screwed directly on a 1.25" to 2" adapter in front of the T2 Baader Amici diagonal.
Interesting. I use the same flattener with a GSO diagonal in a 600mm refractor. How does the Amici diagonal handle the steep light cone?