I agree that drilling is easy, and you don't need to be worried about the breaking of siphon and overflowing the tank like you do with overflow boxes. Its all-out using gravity to send water to the sump, not siphon.
I have used the overflows, CPR, and others, but once I found out how easy drilling is, I never went back.
The CPRs need a pump to with draw air out or siphon breaks,
Above I am using the venturi tube on a powerhead to keep air from building up in the CPR siphon chamber, and breaking siphon.
As you can see, they are easily installed on the tank end.
Below another type overflow box mounted on the end of a tank.
I still prefer to drill though, I just take down the water to below where the hole will be, and drill with the fish in the tank.
You need a diamond coated drill bit, a template, and water to cool the area.
I prefer drilling on tank ends, so the return water from the sump enters on the opposite side mimicking the flow of a river across the length of the tank.
