a great technique to keep in mind

[azz]

a. This is a great technique to keep in mind when arguing with narcissistic people.

Is that sentence slightly ambiguous?

Is it a great technique per se which is to be used when you are arguing with narcissistic people? ( [a great technique] which is to be used...) Maybe it is also a great technique for arguing with other types of people.

Or is it a great technique only when arguing with narcissistic people?
Would a comma after 'a great technique' change anything?

b. This is a great technique , to use when arguing with narcissistic people.

Many thanks.

[Phil White]

You changed the sentence when you added the comma, and the result makes little sense with the comma.

• This is a great technique to keep in mind when arguing with narcissistic people.
  This is fine, and means that the technique is specifically for dealing with narcissistic people
• This is a great technique, to keep in mind when arguing with narcissistic people.
  This is the comma I think you intended, but it simply does not work. Syntactically, the "great" and the "to + infinitive" belong together ("great to keep in mind"). You cannot put a comma between those two parts of the construction.
• This is a great technique, to be kept in mind when arguing with narcissistic people.
  You could probably get away with that to carry the other meaning you suggest (the technique is good per se...
• This is a great technique, to use when arguing with narcissistic people.
  (Your proposal for a sentence with a comma.) This suffers from the same problem as the second sentence above. The comma separates two parts of one construction: "great to use". It simply does not work.