My vote would go for an adjuster capable of being held by a spanner or an Allen key, with a locknut on the outside.
A member of the "If in doubt, build a brick mausoleum" brigade..
(Having set the adjuster, hold to prevent rotation, and tighten lockinut. Even then, backlash in the thread is likely to produce a change of setting).
Failing that +1 for fine fishing line in the hole before inserting the screwed adjuster. Locks the adjuster, and easy to replace the locking medium when it wears/fails.
Howard