I'll take Fast's word for how much quicker it is. The video didn't make that obvious.
Really? The video is 12 minutes in length and I spotlessly cleaned half of a 39' sailboat in that time. That included getting into my gear at the beginning of the clip and then swimming back to my inflatable after finishing the hull, dropping the Remora off and then swimming the entire length of the boat and starting on the running gear. Maybe you have a different idea of what constitutes "quick" than I do.
I suspect the unit is positively or neutrally buoyant?
The machine weighs about 8 pounds dry. In the water, it is slightly buoyant.
Can't tell from the vid if it's as gentle as necessary to avoid removing excess paint?
Again, really? Do you see paint being removed in the video? No, you do not. With the proper brush selection and rotation speed, Remora is even gentler to anti fouling paint than cleaning by hand. It certainly provides a more consistent cleaning than doing it by hand.
To make economic sense, one needs to have business they are currently turning away to fill the freed up part of the day, or just value going home earlier.
Not so, and if you were a hull cleaner, you'd know why. This is a very physical job and having a machine take much of the effort out of the work means you aren't putting the wear and tear on your body like you used to. One of my buddies who bought one told me after his first day with it that he just added 10 years to his career.
Of course, there is also an increase in productivity. It's not much of a stretch to say the Remora can add a boat a week to a diver's productivity. At that rate and at our prices (here in the Bay Area), it will pay for itself in less than 6 months. Mine certainly has.