Use of "this reviewer" in a review
It refers to the reviewer writing the review. It's not that widely used (and personally I don't like it), but I have seen it in reviews, and as a native speaker I don't find it that unusual. It allows the reviewer to respond in the academic third person (a bit like saying &quot;the authors&quot; in a paper) - a grammatical construct to allow them to write with an academic tone.
Personally I just say &quot;I think&quot;!