People "bash" them because they are a poor design, and/or experienced first hand the well known problems they have. They can not maintain a siphon on their own and require a pump to do so. A U tube overflow has no "moving parts", nothing that needs to be plugged in. It works totally on the laws of physics.
And FWIW, I had one with the required Aqualifter, and the prefilter. It failed twice in 3 months form an air nipple clog, which is a common type of failure. I verified proper installation with CPR tech support. Their answer was to check it regularly and poke out the clog with a paperclip. :lol: No thanks.
CPR and Lifereef both earned their reputations.