Inversion tables are a waste of money. Point being, there's too much to screw up decompressing the spine because of all the parts in between the feet and the area they are "decompressing" due to hip tilt (lateral, not ant./post.), leg length differences, blah, blah, blah. The best thing on the market are Back Revolutions. The set-up is more effective, easy to use, SUPER effective by eliminating any movement/variance in the legs and hips and takes up less space. Obviously, clients with glaucoma should avoid any inversion. The website has a ton of helpful information and if you want to know more about my experience using a backrevolution or exercises to do with one- ask away.
http://www.backrevolution.com/
You're welcome for saving you time and money while making you a better trainer.
-Dustin