Justin,
You shouldn't bash a product you know nothing about.
You need to try the wax on your own house and see how it works. I use it on my house, have for several years, I know it works. When I spray it on, water will just sheet right off, you can instantly see it. Bird droppings will also rinse right off. And for the windows...it is in fact similar to rain-x......the water beads right off. On my house, the effects lasts about 3-4 months.
I include the wax as an optional item when I quote a house wash. 9 out of 10 will agree to waxing after the benefits are explained to them.
Maybe you are a part timer and you don't realize the need to maximize the $$ on each job.
For me, doing this full time, I need to make every job I do as profitable as possible. If there is an opportunity to sell additional services or products, I take it, as most people who are serious about their business do.
Every service and product I sell I also use myself. What better way to feel confident selling something, than having first hand experience on your own stuff?
How can you even question what constitutes a harsh environment to vinyl? Don't you know?
Regardless if you can get it clean, vinyl is continually being damaged by UV rays, acid rain, bird and spider droppings, etc. The wax basically acts as a sacrificial layer. The siding will look better, longer.
I liken it to applying a product like Armor All to the dashboard in your car. No it doesn't last forever, but it does look really good for a period of time.