I just bought a bottle of Turtlewax Clearvue Rain Kleer ( rain x clone), which works absolutely fine.
At low speeds wipers do their work many many times better, a single wipe and all the water has run off.
At high speed above 60 mph you don't need to use your wipers at all any more.
Put it on my windscreen about 40 days ago and it's still there working ( even though on the bottle it says that you should repeat the process every 2-3 weeks).
Bottle is fine for doing your windscreen at least 6-7 times. At 10€ per bottle which lasts 8+ months I just went for that rather than better expensive wipers...