Using Variable Neutral Density Filters In Bright Sunlight

Gary from F8 Photography and Mikey from Lightenupandshoot have crossed paths while traveling through Hong Kong. Lee and I ran into Mikey out at WPPI in Las Vegas a few months ago where he told us of some up coming adventures he had planned for Southeast Asia. These guys are really laid back and excited to break out into a photoshoot at any given time. In this video they take a ferry over to a local island to capture a few images of some friends they made in Hong Kong. Around 2:30, Gary talks about using a Variable Neutral Density Filter to almost completely destroy the ambient light while still shooting wide open at f1.2 and maxing out his shutter sync speed at 1/250. I've never attempted this technique, but it has been made famous by many photographers including Joey L. Does anyone have an opinion about these variable neutral density filters or use this technique in their own work? If so feel free to post an image in the comments below.