My gut is going with what Uny said... they probably are of help, but nothing in comparison to actually being on the earth. Considering you're not going to be able to sleep outdoors all the time, getting one may not be a bad idea, but it may or may not be a good investment of money.
One things for sure, though. Actually standing on the earth with you feet is the top of the mountain. Shoot for that and no excuses is what I'm employing. I'm making sure I do it at least 15 minutes a day every day for the rest of my life.