Oxygen Concentrators?

Is anyone using an oxygen concentrator? Are they just as good as buying pure O2? I'm thinking about a medical grade ozone generator but I'm worried I won't be able to get O2.

I've been told I can get it from a weld shop. I would have to lie in order to get it and I'm not a very good lier. Can I get O2 from a Scuba shop or do I need a Scuba license? How much does the O2 usually cost and how long will a tank last?

I'm also thinking about getting an Air Ozone Generator. Do I still need one of these if I have a medical grade unit? Are medical grade units OK for adding O2 to my bedroom while I'm sleeping?