I'm always very skeptical of products that advertise incredible results... as long as you keep using the product for months. If I don't see results in a couple days, I get annoyed. There's a large mental hurdle for me, and it takes a lot to get me to buy a product with these kinds of claims; there are too many scams in the world to not be very careful what you buy.
One product that got over that hurdle for me is this Tilex shower spray that claims that if you use it every day, you'll never have to clean your shower. This product is relatively inexpensive, easy to use, and if it actually does make it so that I don't have to clean my shower, it's a big win. I absolutely hate cleaning my shower.
A product that did not make it is Rogaine. To actually get to the point where you're supposed to expect results, you have to buy quite a lot of it, and use it every day for a long time. And you're not even supposed to expect results, "some people" see results. After a couple months, if it doesn't work, I'm sure they have some kind of satisfaction guarantee, but I can just about guarantee that it wouldn't be worth the hassle, and I'd be out a lot of money.
I just have a soft spot for instant gratification. Now!