Does anyone have experience with Open-Aire Portable Oxygen Concentrator?

I'm looking for user feedback on the Open-Aire Portable Oxygen Concentrator. I know they have a website but before I get sucked into a 30 minute phone call with a salesperson, I wanted to get actual user feedback about the system in terms of it's portability and cost. I'm hoping to get more realistic feedback than the testimonials on the website.