The big knucklebooms have their place. They are nice to deliver something on the flatbed(drywall/ sewer boxes etc.) and then you can unload the truck. They don't work as well as a actual crane, in repetitive cycles. They are horribly slow.
We set a lot of trusses and steel. If you have a good crew and they're moving you can set a truss every 3-5 minutes, and most of that time is them nailing it, and hooking up the next truss. With the crane, you can pick a truss at 20', and set it at 80', and cycle back and forth. You can't do that efficiently, fast and smooth, with a knuckleboom.
Also, their outrigger spans are a pain, the one you have pictured is too wide to set in a standard driveway. Some of the new boom trucks are that way too, its a cheap way to engineer it to gain radius, it just doesn't work in the real world.
A knuckleboom is handy to reach under a overhang or in a door. They are kind of nice in a mechanics truck. But for real world lifting, and placement, knucklebooms aren't a ideal choice.
One of the real pushes behind some of the large knucklebooms, is the certifications required for crane operation. They aren't usually required for knucklebooms, so its a way to place items, but not need to have the operators certified.