I saw an item at an aquatics store a couple months ago that was kinda similar. Basically a large swim fin that both feet go into. It looked cool and was only a couple huindred bucks (iirc), not the $1800 that the article mentions. I’ll see if I can find a link to the product.
See my post 21. That's a monofin. The main maker is Finis, and it makes three main kinds of fins. There's the "Shooter" fin, which is good for training butterfly stroke. There's the "Trainer" fin, which is a narrow but long fin and very good for strengthening the core; I have one of those. Then there is the lovely, incredible, fabulous Competitor fin, the big wide fiberglass beauty which, it sounds to me, is like the one you were looking at. I have one of those, as well.
Two other kinds of monofins from Finis are much less expensive and a really the best way for novices to learn the fun of them. The Tempo and the Rapid. I am going to buy a Rapid as soon as I can -- my other two fins are carbon fiber and fiberglass -- one can really only use them in large pools (or the ocean), the deeper the better. The little Rapid and Tempo are soft plastic and won't threaten to slice another swimmer's leg's off in a shared lane! (been there, done that!!!)
Understand that in true monofinning, for best results your arms should be streamlined above your heads, elbow locked -- second choice is to put your arms at your sides. If you attempt to use your arms as you would in a butterfly stroke, you will only slow yourself down unless you are using the Shooter fin, which was designed to help swimmers learn the rhythm of the full butterfly stroke.
I am a finfreak of sad proportions! Been pretending I'm a dolphin (I even have a broach cetacean breath-take of my own invention as I roll through the water) with monofins and regular fins for about 15 years. I'd love to try a lunocet in a large, deep, warm, clear body of water.