I don't have my log book in hand at the moment but I think they last me 3 or 4 years. I clean them regularly to remove any built up dirt/crud.
I just recently saw a YouTube guy do a test on a lot of wiper blades and the Rain-X came in No. 2 behind a very expensive blade. The Beam blades performed the best in "His" testing, as the water didn't go over or through the Blade/structure, making for a clearer View.
Here is the Link: