That boat in the original video looks like it is pretty close to planing. Definitely a guy in good shape and I doubt he could keep up that pace for long, whatever speed he was at. IMO he :could: be exceeding the normal max hull speed that we are all stuck with though, which is usually 4-5 mph.
A friend of mine has a couple of those Hobie Mirage drive kayaks, they are neat but limited. It is nice to have your hands free for fishing and be able to steer with the little rudder lever, especially when it is really windy. I would say the top speed when you're really pushing it is the same as I can achieve when I'm really trying to get somewhere in my 14'x25" pirogue, which is much faster than most commercial boats I've been in. You're not going to keep that speed up for more than a mile or two though.
I also agree that for long distances a paddle will be more efficient, and I believe it is because of the "glide factor." When you're paddling at a mild pace, you make a paddle stroke, then lift it and glide for 3-5 seconds before making another stroke. If each stroke takes you one second, you're effectively only "working" 20% of the time. With the peddle systems you're spinning constantly, there is no taking a break between strokes, so you're working 100% of the time. Even if your legs are 2-3 times as strong as your arms, that's a losing battle when it comes to efficiency.
The major exception that I can see are open coastal areas with high winds and strong tides, where you do have to work as hard as you can 100% of the time. I've been through inlets where the river was white capping from the tide ripping out so hard that if your paddle wasn't in the water with all of your force behind it, you were going out to sea. This was with a pair of fit 21 year old guys with a lot of paddling experience. In situations like that I would prefer the peddle system, because you can keep up max effort for a bit longer. Compare doing push ups to riding a bike up a steep hill.
The biggest problem I had with the Hobies was that the boats themselves really weren't designed to be paddled. At 10' long and 34" wide, I stood up and took a leak out of it on a gator-infested lake, but they paddle like a Jon boat, which is to say they don't. When we got in the weeds and hydrilla it was absolutely terrible trying to paddle it, where a regular kayak or canoe isn't a problem. I think adding that system to a boat already designed to paddle well it would do much better.