In a nutshell:
OMM made a name for themselves when they came up with rear suspension compatible racks. This opened new doors for avid mountain biker looking to get out for overnight trips and offroad touring. The Sherpa is the little cousin to the larger Cold Springs rack.

OMM instalation instructions

Load Capacity: 40 lbs. 
Weight: 900 g
Length x Width x Height
11.75" x 5" x 14.25"
Available in DISC/ROAD/29" and 26" sizes