I have one and found that it really depends on the day for me. I do not let my arms hang overhead, I kind of lock them to my sides. You really need to start of with less of an angle. Even a slight angle is causing decompression of the spine. I started only at 10 degrees and did that for over a month before increasing it to 20. I can and have in the past did complete inversion, and it really depends on the day for me whether or not it causes me problems, kind of just like any other activity with TOS.