The Mustang is Bontrager's top-notch disc-only rim. The OSB (offset spoke bed, or just plain old asymmetric to us mere mortals) construction means that the tidy eyelets sit to one side of the rim, reducing the amount of dishing that has to take place to keep the rim central. It makes for a stronger wheel, because spoke tension can be kept as equal as possible on both sides.
The quality is superb, and a pair of the rims have built up into a light wheelset that's proved plenty tough enough after several extended deliberate clattering sessions. The faff-free dedicated tubeless kit also available is an added bonus.