There are several things in consideration in this discussion I would like to point out:

a) It takes just one newbie/corrupted/ignorant tribunal to wrongfully screw you big time while you are retrieving your cabal item.
Main difference with other cabals - this can be done out of pk.

b) Manacles render mages 99% useless (shifters are exception) while have almost no effect on other classes.

c) Immortals of CF view manacles as well designed/balanced power and vigorously defend it's current design.

d) Tribbies can call/release guards over and over indefinitely.
To prevent abuse I would put at least 3 ticks delay before you can call for help again.