The math section on the HESI isn't anything to worry about. They provide a calculator, so I really would just focus on refreshing on conversions and fractions. Those were the 2 things it had been a while for me, so I needed to study them.
I enjoyed my time at Watts. It's very difficult, but I didn't have to worry about passing the NCLEX because they prepared me so well. I also basically hit the floor running when I started my first job. Watts grads have a really good reputation in the Duke health system, which can be a good and bad thing. Everyone is always watching (and will report back) BUT it also really helps you get your foot in the door.