Calling it "nonviolent communication" is a brilliant marketing move, as it implies that not conversing in this manner is violent. I've seen this style many times in my career, and it always comes off as patronizing. It also tends to be used far more often than recommended. Instead of being deployed in difficult conversations, it gets used in every one-on-one. My guess is that NVC ends up like power posing[1]: pop-psy…
The problem with “power-posing” was that it made specific (and incredible) claims about the results of using it. I have not seen so much in the book (or if I did I ignored it), and regardless of whether it has any effect on others or not, I've found it valuable in my own mind to have mental clarity, separating observation from evaluation, thoughts from feelings, requests from demands, and simply being aware. (Even if I don't change a word I'd say... actually I can't get myself to speak that way often as it feels unnatural, so I'm content with simply saying whatever sounds natural but with these distinctions in mind.)
There are definitely superficial similarities with a “patronizing” style or a manipulative one. Nevertheless, I do think that, genuinely done, it's more than a “style” of communication, and one for every conversation where there's any emotion involved (not just difficult ones): I see it not as a strategy or technique, but as a reminder that the person I'm communicating with is a real human being with needs — the goal is a greater connection between people, not being more effective at getting what you want (for which I suspect many of the same principles may apply, but employed merely as tricks).
Of course I only remember/manage to put it in practice a small fraction of the time, and I don't know whether the “effectiveness” of such conversations is positive or negative (in terms of outcomes), but I definitely feel fewer negative emotions and that's valuable in itself (to me).