Moi Aussie: And Rav Menasheh Klein has an 18 (I think)-volume set of Teshuvos usually called Mishneh Halachos. That is what is being debated here.
The most random, most unexpected, and possibly most amazing Haskama ever, by the way, is Rav Klein’s on the first Chelek of R’ Yehudah Hertzl Henkin’s Shailos Ut’shuvos B’nei Vanim.