Nope, no drilling needed if you go with a hang on overflow.
I have ALOT of tanks and the biggest regret I have is that I didnt drill my 125g. I waited over 3 years to finally get a larger tank that was drilled and am beyond pleased. That 125g is the only non drilled tank I own and I didnt realize how easy and simple it was until I got my first one drilled already.
It's really not a major deal and believe it or not its alot easier to maintain with no hang on overflow.I was scared to death before I took the plunge but it is definitely the best way to go. One less piece of equipment to clean and worry about.
that being said, if you still dont wanna go with the drilling the hang on will work almost as well.