You won't find a much published on Brentano's Defense. I did find a 3-page (I think) pdf that mentioned some analysis by Hugh Meyers, but I can't relocate it. No matter...all the analysis was pre-engine and was, in all likelihood, riddled with mistakes.
Looking over the defense with Stockfish showed a few lines that it evaluated as nearly equal, but in the long run, I don't think black's position would hold up against a strong player. That said, in amateur play it might be interesting to try it out, but the same can be said of about any opening.
The following simul game was played in Lincoln, Nebraska by Pillsbury back in 1901. Pillsbury had a rough night, scoring +6 -4 =2. One bright spot was the following typical attacking game which is vintage Pillsbury. Black specifically requested that Pillsbury play the Ruy Lopez because he wanted to test the new defense. Pillsbury obliged and showed him what was wrong with it.