I use a Kyosho Mad Force TRS spring, with enough tension to overcome the unpowered servo. The servo is dual ballraced which helps, and has enough torque to overcome the spring tension with ease.

A TRS is also useful to guard againts servo power lose (broken wire, battrey pack gets smashed out in a crash, etc.).

IMO you always need to run with a TRS (set to overcome dead servo) and an intelligent failsafe.