Rain-X or other?

[Siy]

Hi ,
I have just bought a car with a sloping rear window, which doesn't have a rear windscreen wiper....

Can anyone recommend a substance that I can apply to try to minimise the amount of rain that will sit on the screen? I know of Rain-X - is that the go-to product or is there better?

Thanks

[Siy]

Thanks guys - I went for teh GTecniq... will update once it has arrived, and I have appllied it.
Thanks all