Not true, it just hasn't been properly added like many areas of this site.
I can attest that at lvl 4, you get an AGI Stat effect Up. Not sure of the ammount that increase is by but I presume aditional levels continue with this trend
I maxed it out to lvl 20, hoping for another +1 movement. It does a slight increase every few levels. Current agi 62, drops to 56 when I unequipped the ability.