The heavier of the two, XO Trail, employs a four-piston caliper design to boost the power as high as possible. We haven’t seen four piston brakes for years, not since the days when the Hope M4 was my favourite brake of choice.
Important changes that most will welcome include simpler and better sealing around the lever, making, hopefully, for less bleeding. Pivot bearings in the lever are sealed, which should prevent them getting a bit wobbly after a while.
Meanwhile, if weigh is a concern then the lighter two piston XO brake will be right up your street.
Both share a new 170mm rotor, for those who can’t decide between a 160mm or 180mm rotor size when building their bikes.