Magnus Angus spells it out quite nicely in the latest review from Fly Fishing and Fly Tying Magazine.
Decisions about how a rod will look influence how it will perform – even a layer of paint on a blank makes a change to the way that blank behaves. Imago have designed their rods to be and to look functional, and the spartan build is intended to inhibit the performance of the blank as little as possible.
Via Fly Fishing and Fly Tying Magazine.