I wouldn't use a HOB overflow. They are too risky and have a chance of flooding. I used a CPR CS overflow for years and hated it. You have to constantly keep it primed and make sure the prime line stays clean.
Drill the tank and go with a glass-holes overflow or a reefsavvy ghost overflow
Agree that drilling is best if you're starting from scratch setting up a new tank. If you're modifying a tank that's already running, though, the CPR overflow--in my experience--is a viable option that works well. However, you MUST use it with a 15-dollar Aqualifter pump because the pump keeps it primed and will restart it in the event of a power outage. I've run one on my tank for years and so far (knock wood), no disasters. It's come through several long power outages and started right up. The trick, as with most equipment, is to keep it clean and maintained and learn how it works.
I agree with Yoda. Jebaos are a great deal for the money, but if your not opposed the ecotech mp-10 is also a great product, but it is much more expensive. I run both and like them both; however, the ecotech has a greater range of available settings and adjustments.
Not to turn this into a debate about CPR overflows--i've already noted that I think drilling or reef ready is preferable if you're starting from scratch. If anyone else reading this is thinking about a hang-on overflow, though, I'll add this. Yes, the aqualifters can clog and, like any pump at any time, can fail. However, you'll usually notice bubbles starting to build up where it pulls in water. The overflow will keep running for a while. I solve the problem just by keeping a couple of spare pumps on hand. As I wrote on another thread, I think hang-on overflows take a bad rap from reefers. They do have some advantages. They take up much less space in the tank; they are easily removed and can be more thoroughly cleaned with a soak in vinegar or hydor magic-klean. And with the new design, you're less likely to suck a critter into the overflow. The next tank I get will be reef ready. For now, I'm sticking with the CPR. To each his own.