I think this thread has gone off topic and like another member suggested, the OP should use the search function and possibly Google for further information. Both these models are AUTHENTIC Samsung devices which vary slightly with hardware internals. The original link to the YouTube video posted was for a "knock-off" variant of one of these models. Should you wish to buy one of these models and are at a local mobile retailer in your area, they will be selling AUTHENTIC Samsung devices as they would not wish to risk their reputation by selling "knock-offs". As to the version you should buy... This all depends on what features you want and what you plan on doing with the device. This decision is up to you and if unsure, Google both models for comparison and as a last resort, speak with the store representative, explain your needs and see what they recommend. Definitely compare both models yourself though so you have a solid understanding of each. I typically do not take information provided by a sales rep with 100% accuracy.
Hope this helps!