Frankly here is my experience with it:

1- None of the serious doctors that I have seen (whether old style or open to experimental) saw this as legit. One of them told me: your atlas move all the time, how are they going to stabilize it?

2- They take so much Xrays that you have something to lose.

Nonetheless I went.

2- The famous clinic I went to is a shady operation. They display the typical features that I have been warned (by my doctors) to be watchful for:

A- They charge a LOT. They promise a LOT.
B- They want you to stop other therapies. RED FLAG.
C- They measured my atlas alignment (after all the xrays) by laying me down on a table and seeing whether one leg is sticking out more than the other. LOL.

Frankly, I have heard so many bad stories. I would steer away. I would try a regular chiropractor with no BS. Do not let them twist your neck. Just gentle.