There are a couple of the Geared Up boats running around down here in South Florida. At least one Dusky 33 and I have seen the Mainship and a couple others.
Like anything else having to do with boats these set ups are compromises. There are some good features and like anything else this is not for everyone.
The concept is proven, the components proven reliable, the boats go from A to B with reasonable economy. There are some handling quirks like the speed is constant for both props so when you have one in forward and one in reverse you can't increase power to just one prop.
It's not for everyone but it is not a "mad idea" by any stretch.
Steve