adderal is a stimulant. Generally, stimulants increase attention span and concentration. Now it does depend quite a bit on how the stimulant works and how receptor specific it is as to whether it effectively increases attention span and concentration. Adderal is effective, but its method of action and metabolism (both it, its metabolites and products of activity) does create some neurotoxicity (as well as increasing attention span and concentration).
Neurogenex works, in great part by decreasing neurotoxicity and increasing neural metabolism.