I've used it, and like it a lot better than rainx. The application isn't nearly as finicky as rainx, IMO. With rainx, I've found that if you don't apply it just right, it's easy to get streaking and hazing, that's especially noticeable at night. Aquapel goes on, wipes off easily, and doesn't haze or streak. Plus, it lasts and lasts. The only drawback is that it's noticeably more expensive than rainx, but I think it's worth it for the improved performance.
The easiest and cheapest place to pick it up is on ebay. It will usually go for $4 to $6 per application, on average. I agree, pick up several applications per vehicle you plan to do, so you can save on shipping costs and get a better price. I only put it on my two vehicles (don't detail for $), and last time I ordered, I picked up 6. That will last me a good year and a half before I half to order more.
John