External Overflows

[Pan]

Just a quick question on cpr overflows or any external overflow for that matter.
Are they okay...i mean i know having a tank drilled is the optimum, but if that is not an option with a tank are these the way to go? or is like an enheim wet/dry a better choice? instead of an external overflow with a sump?

Are the people if they are using an external overflow...suitably happy with them?