Every so often when a manga does well enough, or the franchise is popular enough, a compilation of a few volumes of the manga are released together as one book. Despite being only two volumes in, Viz Media has chosen to release both volumes of the Tiger & Bunny manga together in one package under the name Tiger & Bunny: Comic Anthology 2-in-1.
The anthology does go for cheaper than buying the two manga volumes separately, as it only costs $12.99 US/$14.99 CAN for this book while buying them individually would cost $20. To see whether or not these two manga volumes are worth picking up, you can check out my review for Volume 1 here and my review for Volume 2 here.