RainX is a kind of micropolymer in a solution with tonnes of filler, that is basically supposed to make the glass so smooth that water beads up on it.

I have used it for a quite a while now on multiple cars. About the only draw back I can see about using it is, if you don't buff it off properly, it will smear and smudge. It works wonders in the wet. In fact, with sufficient rain and speed, you won't even need wiper blades because the rain is sheeting off so quickly.

As for its longevity, that is totally dependent on how much rain you get, how dirty the driving conditions are, and how much you use your wiper blades.

I doubt that this stuff will work to really quiet chattering. The chattering is occuring simply because the silicone-rubber is oxidizing. If this is the only problem, why don't you just replace the rubber part of the blade if you are using oe wiper blades? Places that carry bosch stuff should carry blade replacements for about $5 each.