Whenever reviewing Low-Quality Posts (Answers) I generally choose to comment if appropriate situation is detected, But if a comment is present on the answer already, should I select No comment Needed option?
Oh, hello there! I see my name. Cool.
What should happen is that you select an existing comment and the existing one gets upvoted.
What does happen is that a second comment gets posted. Meh.
So, while we're grounded in reality instead of our ideal fantasies, the best course of action is to upvote the existing comment and select the No Comment Needed option. See Eliah's excellent writeup (let's ignore the fact that the words "Eliah" and "excellent" are redundant) on this topic.
If you see this happen, feel free to also flag the later comment as obsolete/not constructive/a duplicate. They're basically free flags at that point.