I’ve found the frames for the Flow Hive Complete are narrower than the frames for my Mediums I bought from BeeThinking, but even those I could fit 9, but they need shaved down or else your outside could risk rolling the bees as was described to me - My Inspections - A rolling update every time I crack the hive with new photos and as also discussed in that post you don’t always need a Follower Board as not ask bees will build goody (I think @Dawn_SD said 1 out every 4 hives will need a Follower for her).
P.S. I’m still learning so others may correct me still.