There are three primary problems with what I see in this video. I base these arguments on the 3 years of American Sign Language I studied in University, and the thousands of dollars I spent drinking and talking with Deaf people and other ASL speakers. I'm by no means perfectly fluent, but I get by. Beer helps.

First issue: The signing they are doing in the video is very simple and limited. Not just in the number of signs, but in the complexity of what they are doing. Their face remains perfectly neutral. They move slowly and carefully. They are signing individual signs one at a time. That's not how a signed language works!

Signing without facial expression is like speaking in complete monotone, making no eye contact with the person you're speaking to. You can probably get your point across, but you're not having a real conversation, and you're missing something important. The lack of flow and motion to the signing is also awkward as hell. In short, the people in those videos are not actually fluent in sign, they're trained actors who have memorized certain motions.

Second issue: There are concepts in sign language that have no equivalent in English, or many spoken languages.

One example- in ASL you have variables/registers, in the programming sense. You can sign "John", then point to your left. From now on in this conversation, if you point left, you mean John. If while you speak, you want to describe John moving to your right, you can do that (explained next). Now pointing right means "John".

How might you 'move' John to your right? You could have a single finger pointed up, like John was a finger puppet, and walk him to the right. If he got into a car, you could have that single finger get into another specific hand form that generally means 'vehicle'. Then you could draw a tree with your free hand, and drive the car into the tree. You just told the story about John driving into a tree. There were no specific nouns or verbs used. This is how a lot of conversations work in ASL.

The point I'm trying to illustrate above is that description and conversations happen very differently in signed languages than they do in English. It isn't that the words come in a different order, it's that the idea you are trying to communicate is explained in a completely different way. You're comparing apples and coconuts.

Third issue: every city has its own dialect. Signed languages aren't written down, there isn't much global media of people signing, and the result is that dialects change constantly. Drive to any other major city, entire words have changed. Talk to a family across the street, they might have different signs for some words. Sure, the core language is the same, but you've got a lot of different nouns and verbs.

Going even deeper, some people here have already mentioned the difference between ASL and Signed English. Some people sign English words one at a time in the order of English grammar. Some people go into the 'pure' ASL realm, as I described above, and use very complex concepts not used in English. It's not a choice, they'll have simply learned ASL that way. Most people are somewhere in between the two extremes, and it's a continuous domain, not discrete, with a huge variety.

I won't discourage research into this, and I think what they're doing is awesome- I considered doing a master's thesis on this exact idea. I just want to put a nice big disclaimer here that this isn't useful yet, and there's a long way to go.

Edit: Wall of text much mabbo? Woah man, take a breather.