When held in your inventory the lure makes fishing take place instantly. The drawback is that fishing will train at a drastically reduced rate - skill gains remain the same based on the potential of the fishing skill but will only happen roughly once for every twenty casts. Since the use is automatic, you have to drop if if you want to properly train fishing again. Using the super lure will consume anywhere from 15 to 20 stamina per cast, compared to an average of about 10 when fishing normally.