Do deck coatings work as claimed?
The jury is still out on these types of products.  I was at a contractors day at my local Lowes and the rep from one of the manufactures of the epoxy style coverings was there demonstrating the product. The end result was a smooth, not sandy, but mottled non skid finish. the dried samples on display revealed about an 1/8" coating on the wood. I did spend a little time talking with the rep and he cautioned that the wood needs to be clean and free of any loose decay, oil or grease (like from a BBQ). Any loose nails should be replaced, better if the deck was screwed down so nails would not work up through the new finish.  He did not claim that this was a "fix" for rotting wood or a surface in very bad condition. This product seems to me to be an alternative to conventional sealers or stain. The claim to fame is that it will outlast regular sealers and stain for years. The previous points about spacing and the top of the joists are very valid. My biggest concern is the holding ability if used over bad wood. I think lots of people will try this hoping to stretch the lives of aging decks. Since this product is so new, there are few anecdotal cases with which to compare it. I might be tempted to try if if a customer insists on it, but think I'll wait until I get some feedback from other contractors or users. the cost is also a consideration, it is expensive.