Expandable underreamer with dual blade block where second cutter configuration is a modified redundant arrangement

An expandable underreamer for use in a drilling assembly includes a tubular body and a block 200, 2071A, extendable from the tubular body. The block includes a first arrangement A of cutting elements 203 disposed on a first blade 2070A and a second arrangement A' of cutting elements 203 disposed on a second blade 2070B. The second arrangement is redundant in that it retains the same cutting element positions, but is modified in terms of the cutter exposure, for example. The second blade may have a reverse exposure compared to the first blade to maintain balance. The block may further include a flow channel 204. In a second aspect, a reamer includes adjacent leading and trailing blades disposed on a first block, and a unique blade disposed on a second block, wherein a gage portion of at least one of the blades has a length between 30% and 45% of a total blade length.