Nah, don't bother on a XChallenge.................not worth it
Peculiar to the airshock on the XC, when you brake hard on the road this loads up the front and shifts the weight forwards and the shock extends (no spring).
This takes the weight off the rear wheel and renders the rear brake totally useless on the road...............90% of the time
I've done plenty of emergency type stops and the non ABS bike pulls up fine (just forget about using the brake, unless your bum is sat on the rear rack)
With ABS, this would just increase the braking length, because the rear brake is completely ineffective
Forget what others are saying on other types of bike with ABS, they are not XChallenges and their bike's supension works in a completely different way and therefore their comparisons are not accurate