This is an incremental game with some factory building gameplay, but rather lightweight on the factory part. I completed this game (finished the tech tree) with 10h of active play, without any of the IAPs. It's fair to say they're not needed to progress. As long as you optimize your factory you'll make good progress. It's free, and the IAPs are entirely optional, so I recommend giving it a try if you're interested in production line management gameplay.