The other day I posted about the initial anonymity of Sefer Habris (link). Serendipitously I came across a very positive review of Sefer Habris in Hameasseph 5569/ 1809 (New Series v. 1). The reviewer discusses the anonymity. Note that the second edition, where the author uncloaked himself, had already appeared. However, this reviewer either did not know it, or the review was written before the appearance of the second edition.
He writes that some who know the author have told him that it is one Rabbi Elijah of Vilna - but not the famous, deceased Chassid Rabbi Elijah. It's another Rabbi Elijah of Vilna, albeit which family he is from is unknown to him. He says that the author had spent time n Berlin and other German cities. He adds something interesting in the a footnote which is that once it was known that he was the author, there were some who were skeptical, as R. (Pinchas) Elijah wrote in the introduction to his second edition. There the author had written that some thought it was too much for one person to have written. Here the reviewer says that in conversation some people found that he was not as scientifically knowledgeable as his book implies! But he says that this doesn't mean anything, because he never claimed to be a thorough expert in each one of the sciences he discussed in the book, as if he was formally educated and mastered them from his youth.