It is not at no cost, Johnathan Blow said that it was vastly hardware accelerated by the GPU due to having different blocks dedicated to its implementation, so its far easier to implement and at a significantly lower cost to the rest of the graphics rendering pipeline, but its not 'free'. Some engines don't play nice with it.
I would argue to say that its not accurate considering we only have youtube compressed videos and low bitrate footage months before launch to go on.
According to Richard of DF also, devs have varying degrees of implementation going on, with the Horizon footage clarity wise being the best first party wise right now(i'd agree, viewing the gamersyde footage on a 1080p TV via file format), Tomb Raider being the best third party wise, and Deus Ex's implementation currently being the worst.