I have one and used it on my 15 hour TA to Italy in October and on a 5 hour Transcon in November. It does take up quite a bit of space but it has its own bag.

I did not find it comfortable as a full back pillow. I am short, 5'2", and the I couldn't get the headrest in the right place. Also, the way it works is you shift your rear up to the very end of the seat and your feet go into the storage well under the seat in front of you. That may be OK for taller people, but I didn't find it comfortable. I had to use my carryon as a footstool, which I normally do anyway, but it still wan't great. For others, you are going to give up that storage space. It makes you sit with your back fully straight, so you can't lean on the window, if you're used to doing that.

I found it to be the best lumbar cushion I have ever used, however, by inflating it slightly and folding in half, as the instructions suggest.

I got it on sale for about $15. I don't know that it's worth $30, however.