If you research Overflow boxes, you will find that some of these things leak, and some lose prime, etc., after a power outage, etc. Some even need a pump, just to prime them back up.
I would suggest to take a look at the LifeReef overflow. They are build like a tank, and are very under rated, meaning, you can power a more powerful pump than advertised.
These overflow boxes, have been known to keep prime for years. That's right, years. I have one of them and they are awesome. I have not seen a negative comment on this product.
New, they are not cheap and sometimes they can be had in the f/s forums. They go quick.
BTW, I have mine, in a 55 gallon reef tank.
Good luck.