I haven't tried it (I'm registered, no joy) but I'm skeptical of its utility, to me at least, because it replaces writing code with reviewing code to identify whether it does what it should and fixing it if it doesn't, and I find the latter vastly more time consuming and mentally taxing than the former.
At any rate, I was also initially somewhat skeptical but it is hard to overstate how effectively it predicts exactly the code I was about to write, or suggests the code I don't know I want. It is, for me at least, significantly faster in the languages I know well, and monumentally faster in the languages I don't know well.
I'm keen to try it out just as soon as they let me.
It also helped me learn new features or ways to do certain actions. One such case was how it used immutable data structures to represent a change rather than mutating. Think `arr = [...arr, newElement]` rather than `arr.append(newElement)` which is not exactly the code I was writing but simply an example.
The positive comments I read from people who've tried it give examples of things it's done right, effort saved, things learned, but make no mention of the effort taken to verify what it produces. I don't know if that's because they're uncritically accepting what it produces (which would be bad), because it's only usefully producing trivial bits of code (which would put it in a race against how fast I can type, handicapped by whatever percentage of the time it gets it wrong and the time taken for me to check) or because I am somehow unusual in finding reading code much, much harder than writing it.
I'm getting pretty frustrated with the limited access. I signed up months ago. Just release it already.