Double pull levers require twice the effort at that side for the same result. If you have an injured or weak hand they are very usefull. A rear brake can be exceedingly dangerous on a tadpole trike like a Warrior. It's perfectly easy to do a stoppie with good disc brakes on the front meaning the rear looses traction. Braking hard whilst having some steering input with a rear brake can easily have the rear overtaking the front. Fun if you are expecting and wanting it, but lethal if not .