They seem like a great idea until you learn and understand how they handicap your critter spotting abilities. Yes, the best idea is to always carry and use a flashlight.
A red filter overcomes the blue tint of the water. It can make large scale panoramic views quite pleasing.
Red filters also increase contrast. Critters utilize contrast, sometimes to hide in plain sight. Contrast is another word for the distinction between light and dark. With these filters, you essentially blind yourself to nuances in the gradation of light that allows you to perceive lurking critters. You're going to be blocking your perception of mid range lighting values.
in early days of Hollywood (until the 1960's), moonlight sequences were shot in b&w during mid-day with a heavy red filter. It increased contrasts, turned shadows to black. Nice effect, but a great simulation of night blindness.
The recent explosion in "special red filters" for u/w cameras is kind of amusing. CC30R or 40R filters have been available mail order for 60 years from places like Porter's camera, or you can pay $65 for them from a dive camera website. They used to be a standard $6 accessory for every Nikonos 35mm camera toting diver.
Physics and filters haven't changed much, but new marketing pitches increases interest and apparently the price s well.