Rengar, yes. Irelia, no. She wants constant attack speed so she can use Hiten Style often, and doesn't build any real AD so the crits won't do much.
Neat trick with Udyr - Activate it in Turtle stance and bombard the enemy with constant high-speed critless attacks, then switch to Tiger and unleash 3 devastating 2.5AS crits in a row. Very powerful combo.
Also quite nice to make use of Xin's penetration and quickly proc a knockup.
Try it on melee carries too. GP's Q becomes a guaranteed crit, Master Yi can use double strike on top of the AS, and Fiora can burst down an enemy that little bit faster. --- Evelynn is my waifu. Help... Me...