From the link:
Factorio was developed for 10 years with only keyboard and mouse in mind, so making sure the game is fully playable with controllers was no easy task. Playing with a controller is slightly slower, and will take some getting used to (just as it does when playing with keyboard and mouse for the first time). After becoming familiar with it, I find it very comfortable. I recommend everyone to play through the first levels of our tutorial campaign, as it's a great way to get acquainted with playing Factorio with a controller.