Ah, the hot debated ED glass.. Lots that have been said here is true and accurate. That said FPL-51 is a good performer in its own right, more so if your a visual observer.
Also fair to say the focal ratio of the scope has another performance effect. My ED 80mm is indeed FL-51 with a focal ratio of f6.8 as a visual observer this max's out the performance of the 51 lens. The only slight CA (yellow fleck) that's noticeable is when I point the scope to Venus.
I post this for newcomers who are visual observers on a budget. FPL-51 is a good performer, and should not be dismissed.