Rain X works great for me. Afterall, they are the ones everyone else is trying to copy
There are any number of superior products out there operating in this area, they just don't have the marketing force that supports Rain-X. It really should not come as a surprise but a big marketing budget is almost certainly more important than a good product (and I am afraid that this extends to 'detailing grade' products as well).
Our experience is that, most of the time this type of product (not Rain-X, that is a totally different product type) fails, it is down to the preparation. I realise the OP says that he followed the instructions but what precisely was done? We have had people tell us they totally cleaned and decontaminated only to find that means that they used a non-abrasive cleanser and wiped with vinegar. For optimal performance of any of the higher grade glass products, you ideally need to do a machine polish with an abrasive product which is free from silicones of all kinds (because they are really tough to get off after) - this will ensure that you remove any previous coating/product on the glass. Hand polishing and non-abrasive cleansers are not enough, often such things will fail to remove even rain-x. After this you need to remove the polish residue, particularly the oils. It might look clean but polish and compounds use low volatility oils which keep the product workable but the flip side is that these oils will persist for some time (hours, even days) after you have buffed off the visible residue. To get shot of these, you need to get out your volatile panel wipe or IPA and do several passes and ensure that you give adequate time for it all to evaporate. Only then can you be confident that the surface is truly 'clean' glass.
To put in context, we have a product which is a glass cleaner but gives residual water repellency (a bit like rain-x). It is not massively durable and you rarely get more than a couple of months before it isn't really helping you. If, once it starts failing, you give it a clean with APC and wipe with IPA and then follow up with our long life sealant (which is 18 months plus) - the long life sealant will almost certainly fail within weeks. The reason is simple, inspite of the temporary product having clearly begun to fail and a thorough clean having been employed, enough of it remains to get between glass and the higher tech product which then cannot bond properly. This is something we have reproduced with a number of products and our view is that most of the high tech products understate the need for preparation. Of course, if the OP has gone to this full extent and it still has not worked then I am lost because, assuming the surface is genuinely clean, the product simply not working is a bit like jumping out the window and finding that you aren't falling - it goes against nature!
