The thing with outriders is: Being vast cav; you can scout them at exactly 24" and an unfavorable angle before the game even begins. With their BS of 4 and multiple shots (*3) they are just as effective as3 handgunners. Immagine a tiny 3-model wide unit of 2 ranks shooting with 18 shots immediately at the first turn.
Buy a champion with BS of 5 to get even more accurate shooting. Just don't be tempted to buy any of the fancy weaponry; their repeating hand guns are statistically the best.
The best thing of them is: they don't automatically die when charged by infantry. Being fast cavalry; they can flee and redeploy next turn.