I use a DeVilbiss "Compact" (it's not really that compact and it weighs 12kg )O2 concentrator, which can pump up to 5 liters/per hour and can accommodate up to a 50-foot cannula (15.3 meters), so at least you don't have to move the machine that much.
It's a bit noisy, but you get used to it and now I can do my O2 while I sleep, without the ear-plugs. And I only have to do around 12-16 hours a day, because going away it's not feasible with this.
On the good side, it's very easy to use and reliable, I had no problems at all with it since I got it in 2007.
I don't own the machine, I pay "rent" fot it (it would be to expensive to buy it and not knowing how long it would be needed...), to the company providing this service, but the health system here only covers 40% of the cost, the rest comes from my (parents') pocket.