Again, I'm not familiar with the AS-350. And I do not know why the Astar's control system is apparently designed so that the collective can creep up - or in any direction, actually. Forget about locking it completely down - if there is not a device that adds enough "general" friction to keep it from moving unintentionally (like, forgive me, the 206) if you take your hand off it, then IN MY OPINION the design is defective.
Friction AND collective lock on all of them
AFAIK.
Too bad that the policy revolved around the flawed understanding of "low flow" issues with the engine as pointed out in the report.