How To Choose The Best Portable Home Oxygen?

High school textbook taught us that, ordinarily, there are two methods can help us get oxygen. One is in Chemical book: mix sodium per carbonate and manganese in water, eventually, oxygen comes out. Another one is in a physical way: keep cooling natural air, till it turns to liquid. This process would require an extremely low temperature, about -183C. In natural air, each element requires different level of temperature. Through controlling the temperature, we can get different elements one by one, and under this way, the elements we get would be comparatively pure.
For home use oxygen, apparently the first way is very convenient and requires simple condition. You just sit there, take a container full of water, and put several bags of chemical ingredients in, cover the container, using the extended tube to inhale. While, besides the uncomfortable odor, chemical elements, in some degree, would be hard to our lungs. Those heavy metal elements may stay in our body, some will be distinguished out by our metabolism system, while, some of them, might stay there forever. No one knows what kinds of effects they would take. On the other hand, the purity of chemical abstracted oxygen could not be very high.
The second way, which is very popular in medical industry, is considered safer. While the limitation is quite obvious: apparently, we cannot make an environment with the temperature of -183C easily with home refrigerator, even in the South Pole. Either extremely high or low temperature requires complicated systems. Not bother to talk about the price of such a unit of machine, only the place it will take is a big problem for normal house. At present, a popular way is to keep an oxygen tank at home, and take it to the oxygen gas station every time the oxygen inside is used out. Normally, hospital would offer such service, while for those patients, who are living in home alone; this way would be quite troublesome. Those who are living far away from big hospital which can offer such service, this it also not very convenient. To rent an oxygen tank, the hospital would ask for some deposit, normally higher than the retail price of the tank, and still you need to pay for rent and their refilling service each time, not to mention the time and gasoline you loss. And even it is medical equipment, keeping a tank with high pressure inside is still a very uncomfortable thing...
Now, it seems that canned oxygen is a good solution to portable home oxygen. It is light and small, very easy to be carried anywhere (except airplane). People can use it the same way to a can of coke. Enjoy the oxygen, and after it is used out, just give it to trashcan and never bother to take it back to a certain place to take your money back. When you need it, it is there for you, and when you feel it is not that necessary, just store it the right way and before EXP, you may use it anytime. The most important thing is that the oxygen inside is medical standard and abstracted in a totally physical way. The same content with the oxygen tank, only canned oxygen is cheaper and more convenient.