I always wonder about the business model of 'free' services:
"FileDuck may show you ads from advertisers and artists selected by FileDuck (such as full-page wallpaper ads) when you use the Services."
"FileDuck is in beta and the basic functionality of FileDuck file sharing is (currently) free from registration and charge."
So, it looks benign at the moment but I wonder if it will remain free for 'unlimited size' file transfers? I'll give it a whirl in any case...