The tetrahedral radar reflector (like the Davis) is sometimes called a rain catcher because that is how it should rigged to be most effective - in a way such that one of the corner "pockets" would collect rain. When oriented in the raincatcher position, the tetrahedral reflector presents the most reflective surfaces to a radar beam, making your boat a good "target" on the other ship's radar. Because this type of radar reflector is a bit big, it is usually onlly hoisted up the mast in conditions of poor visability.
Up here in Foggy Nova Scotia, I have two Mobri radar reflectors permanently attached to the shrouds, just above the spreaders. The Mobri is a sort of elongated terahedral reflector inside a 2 inch diameter plastic tube. It doesn't work as well as the Davis, which is why I use two of them. Other vessels with radar tell me my boat makes a pretty good target.
Radar reflectors in southern waters don't get much use, but when you need one, you really need one! Even a boat like ours doesn't show up very well on a big ship radar.