I owned one of these for years - different model. If you have weak ankles or get queasy easily, this is not for you. The locking mechanism that holds your feet in place has to be tight - and when it's tight, can cause very sore ankles & feet because all your weight is hanging from them, especially if you fully invert.
As for the queasiness, I could only manage to stay on my machine for a minute before I got sick to my stomach. I tried everything (not eating, eating, eating crackers or bread)...but as soon as I was inverted, boom! Sick to my stomach and it lasted all day. So queasy people beware.