FTB brake is not topic in here, but this is how it works:Notice how there's an equal and opposite North-South Polarity. There's no attraction force pulling the brake shoes upwards the spool. I frustratingly proved that to myself by dangling Banks of neodymium magnets next to rotating spool and could not get the moving spool to attract the magnets at all.
Magnets are installed in (slightly) tilting arm, which is connected to pivot point and in the other end there is spring. There's not attractive forces, exactly like in video was said. But there is brake torque. Magnets are in D2, which is bigger than D1, where is pivot point, and therefore brake torque generates arm to be slightly tilted around pivot point, which compresses spring. And cheap Aliexpress reels certainly are not topic in here. But like like said on a video, some Chinese manufacturers have messed up with LeftHand "FTB" reels and they have copied magnet arm wrongly in LH reel. Pivot point is in wrong side, which makes that in those reels "FTB" is not functional. Obviously this issue with non-working "FTB" in Chinese LH reels is large. As I know, it concerns Fishband GH100 reels and Black Knight II and I think these are not only ones. Interesting that Chinese has copied only RH reels and forget that LH is different Not sure but I think Kastking Kestrel Elite is OK also in LeftHand model, and should be, at that price tag.