Just to be clear, since there seems to be some misinformation here …
The two Core books for Tales of the Valiant are the Player’s Guide (384 pages) and the Monster Vault (380 pages). Everything you need to play ToV is in those two hefty books.
The Game Master’s Guide (304 pages) is kind of a quasi third Core book. It is not required but there is a ton of great info in it to help improve your game in hundreds of ways.
The Game Master’s Guide Is NOT equivalent the D&D DMG. The Player’s Guide and Monster Vault contain what would more or less equate to the D&D Dungeon Master’s Guide and Player’s Handbook. The ToV Game Master’s Guide Is for GMs that want to enhance, expand, and improve their skills and their game.
Hope that helps!