Apparently FL-301 Flangers were equipped with two different chips. One version contained the MCI458P and the other a TL022CP chip which some consider inferior to the MCI458P with regard to sound. Some models carried the locking nut on the front end power jack.
So that being said please bear in mind that I have not differentiated between the different versions of this effect. All versions of the Ibanez FL-301 have been lumped into this price listing which may account for the price swings. One review on Harmony-Central can be found here — so not a lot of information on these flangers.