Originally Posted by DaveK
I believe most of the issues coming from the use of siphon overflows come from people using ones such as the CPR overflows, which in my opinion have inherent design defects. If you use a quality siphon overflow, you will seldom, if ever, have a flood due to the overflow. Of course, you still have all the possible flooding issues that can occur because you use a sump, such as the return back siphoning during a power failure, or something blocking the overflow.
Like anything else, it depends on the quality of the original design. There are some good and a lot of bad stuff out there.
My thought about siphons is that they have the inherit quality that, at some point, they will fail because of air ingress. A drilled tank is vulnerable to glogging, just as a siphon is, but it is the loss of siphon that always gets me. An impartial Google search would probably show that that is what gets most others too (if you were to compare various failure cases and did a quick count). I'm too lazy to do that, but I'm betting that you could come up with some quantifiable data on the "badness" of siphon overflows.