Top down hats scare a lot of knitters, even ones experienced in circular knitting. It’s because of the increases needed, I think. However, top down hats are great - if you don’t know your gauge you just increase until the diameter is about 1/3rd the desired circumference (C=3.14159D), and then work the hat normally. If you’re not sure if you have enough yarn to complete the hat (as happened with this one), you can work it until the yarn is gone and then either add on a new skein for the body (as I did here) or make a beanie. Plus, it feels a lot more like a hat than a tube for the majority of the time!