Your opinion: should I learn and use technology in commercial projects?Believe me, worth it. Some financial exchanges (as an example of a commercial project) actively using them. A web socket, it is essentially the most common socket, which is used about everywhere (in 99% of programs) work with network traffic, stranded on top of the web of reality (the HTTP Protocol).
Did I understand correctly that this technology leaves no long queries in the address bar?This technology does nothing to the address bar and does with it not connected. It is a technology for transmitting data on a continuous basis in real time, for example, it is ideal for chats.
you can deduct the vulnerability in the systemIf I remember correctly, the vulnerability is possible in the case of using a proxy ("counterfeit") and lack of encryption.
In addition, the feature of ES6, I thought support would limp and it is more than 90%.Maybe I'm wrong, but I don't remember the connection between the RFC specification and ES6, besides, in my opinion, ES6 appeared late 2011. (which appeared in the RFC specification for web socket).
If anybody had any experience with this thing, and may be put into practice at the current time.Was, I wrote a server and client in C/++, it's pretty much not noticed, the question of time and desire, that would be... detailed understanding of JS frameworks and libraries (e.g. Socket.IO), some actively use web sockets as a replacement for the long pools, flash sockets and so forth.