First of all, what are rubber pool decks? Pool decks are the area around your pool. Often they're made of concrete, but there's a huge variety of materials you can choose from, like rubber. Rubber pool decks use, well, rubber to hardscape that area around your pool. More specifically, small rubber granules (a lot of them) are set with a binder, often polyurethane, to form a durable and slip-resistant surface.
Rubber has become a really popular method for pool decks, though you may be more familiar with it's use in playground surfacing. A lot of playgrounds have switched to using a rubber surface, for safety and ease of maintenance.
Why rubber? Well, rubber pool decks have the advantage that the rubber still has some grip even when it's wet, which is very important for pool safety. Rubber is also resistant to living things growing on it, which means you won't encounter issues like moss or mold that can make some other pool deck surfaces become slippery. It's also really low maintenance, especially in comparison to the upkeep of a wooden pool deck. It also can go on top of an already installed concrete deck, which might be really useful if you're starting to see some cracks in the concrete and are worried about the safety of it. The rubber can actually fill that in and negate its impact on the deck.
Another advantage rubber has is that you can get it in a variety of bright, fun colors. There's also, of course, more natural looking colors that look more like a natural rocky finish, if you want. But there's also blues and teals and purples and greens and so on. You can get really funky with your deck colors, and the colors are colorfast so you don't have to worry about the upkeep you would need to do with a painted surface. (As a note, the color of a rubber pool deck may depend on the Rubber Pool Deck Installation. It can change in the first few days of installation, but this is temporary and will fade within a few days.)
Rubber pool decks will probably cost you about $6400, though this (naturally) depends on the size and complexity of the shape. This is, admittedly, a little pricier than your average pool deck made of cheaper materials, but with that extra money your buying an extremely low maintenance product, which is going to save you time and energy in the long run. If you're worried about the environmental impact, many rubber pool suppliers use recycled rubber or make their rubber granules from waste material that would otherwise be thrown away.