The answer is, of course, video pros or "prosumers" who need to carry around not just one, but several GoPros as well as an abundant supply of housings, mounts, quick-release buckles, batteries, a pole, a tripod and anything else for getting the right shot no matter the situation, and still have room for a tablet or small laptop to handle viewing and editing out in the field.
Ample storage is just one of the reasons why it's worth its $330 price, though. (That price converts to about £230 or AU$430.)
It's a long slim pack, so even when it's loaded up with gear, you won't feel weighed down by a bulky bag as you run from location to location. A set of straps on the right side can get snug enough to hold a pole mount like this one from MicroJib.
The right side has a side access so you can just reach in for your cameras or mounts. A pocket on the inside of the flap is perfect for extra batteries, cables or memory cards. All of the bag's zippers are coated to help keep water and dust out.
Another set of straps are on the left with a pocket at the bottom to hold the legs of a tripod. No tripod? Use it for a water bottle. And if you want to secure something to the front of the bag instead, such as a skateboard, the side straps can connect to each other around front.
Incase includes a thin bungee cord that can be laced through loops -- five on each side -- to secure things to the bag, like I did here with my rain jacket. The cord doesn't seem particularly durable, though. It's likely that it won't hold up over time, so I wouldn't trust it with anything too heavy or important.
The back panel is well cushioned and has channels for airflow. The straps are wide and padded, too, and there's a sternum strap to keep the pack from sliding around on your back. A grab handle on top is just wide and thick enough to keep it from digging into your hand when the bag is fully loaded.
The back panel unzips to give you full access to the main storage compartment. For such a small, slim bag, there is quite a bit of room for multiple cameras and accessories. The bag's exterior is made from a coated water-resistant 600D poly non-PVC and 1680D ballistic nylon and has small feet on front at the top and bottom to raise it a bit off the ground when you go to open up the back.
There are two different styles of organizers. One is weather-sealed and has an interior frame made of Tensaerlite, a foam material developed by Incase that adds a floating, shock-absorbing layer to the case. The other is a simple zippered case with a clear polyurethane window so you can see what's inside without opening. Both come with removable nameplates.
If you're worried about scratching your camera's lens or protecting it from rain and dust in between shoots when mounted out of its housing, this silicone cover does the trick. You could do the same with a simple plastic bag, but this is more durable and, you know, looks cooler.
The top of the bag has a compartment big enough to hold a dSLR or other camera or anything else that won't fit in the rest of the bag. The bottom is just a Velcro-attached separator, though, so if you need one large compartment, you can take it on out. There are three separators included with the bag to break up the storage however you'd like.
The Kelly Slater Action Pack is well-constructed with a lot of storage space given its size. It's generally excellent assuming you have the need for a dedicated bag to travel with your GoPro cameras and gear. The $330 for this pack covers all the accessories and the stylish design and Kelly Slater branding. If you like the bag, but want to save some coin, Incase makes a black version that comes with one accessory organizer for $200. Then you can kit it out however you want, including with Incase's dSLR insert, so you can use it as a bag for GoPros or other action cams or a regular camera.