For my F2P alt account, I didn’t research anything after TC 11, and instead focused on getting to TC20. You need to level up your iron storage though to be able to build this, and your houses to hold enough recruits to use TC20.
Btw - Now I have too much food and iron . As a F2P account, it’s the build times that are the most annoying.
. As a F2P account, it’s the build times that are the most annoying.