As I recall my FD lens days, the FL was the same mount. The FLs of the day were close to todays "L" lenses in quality and price. So I stayed with all FD lenses.
If you haven't already read it on this web site or others, FD & FL lenses are "full manual" lenses. Manual f-stop, shutter speed, and most of all, manual focus. All the adapter 'does' is allow the mating of different mounts, but I do not think any of the electronics in the lens "pass through".