The Bengal Helix 3 comes standard for the Nimbus Oregon unicycle, it is a durable, high quality hydraulic brake, similar in construction to Hope brand brakes. My brake has seen light duty on a 36er, otherwise it is quite fresh. This brake includes the IS adaptor, a new 160mm rotor, and runs on DOT 4 fluid. The line length is 43" which is sufficient for muni or 36er T Bar use.
UDC sells this brake for $120 plus shipping. Get the same brake, lightly used for $75 plus shipping.
The Tektro Comp is a basic hydraulic brake, all metal construction, very durable, I used it for a few months on my 29er. This a decent brake, but it takes a little extra fiddle time and they could use a liberal dose of anti-squeal which can be applied to the pads by your LBS.
This brake includes the IS adaptor, a 160mm rotor, two sets of pads (semi metallic and hard black organic), and runs on mineral oil. The line length is 28" which is sufficient for 24-29 muni use without a handle bar. I have a 34" inseam and run 150-165mm cranks on my 29er and the brake line length is sufficient.
I bought the brake on sale from Chain Reaction Cycles, then purchased the aftermarket pads. My brake is the same as the one pictured at Chain Reaction, but with a silver lever. Get this brake for $50 plus shipping.