The NASA tests were with a two strake configuration, and Westlands Sea King strake was a single strake.
The issue for the Sea King was to provide extra tail rotor authority in a very specific wind condition (right side wind of about 10 knots). It worked quite well.
The NASA strakes also worked for side wind conditions, but didn't appear to provide much benefit in a zero wind condition - which is the condition that hover performance is tested for.
It may make a difference for yaw control activity in many conditions. I can understand Bell's concern for the strake being solidly attached to the boom as it is.
If there is a performance improvement it would be slightly difficult to prove it - a lot of hover performance testing needed.
And I've also see some STC stuff that left me wondering about the qualifications of the persons approving...(say no more)