[TheForge] Oxygen concentrators

[theforge@mailman.qth.net]

There are several oxy concentrators for sale on eBay 
(2381780626 and others).  There was a thread about this kind 
of technology on theForge awhile back.  Could the person 
using these instead of oxy cylinders please answer a couple 
of questions...?

What kind of capacity is possible?  
What kind of oxy storage is necessary to use with standard 
torch set?
Are there comsumables required such as an replaceable cells 
and what is typical cost.
Are the units for sale on eBay appropriate for typical torch 
use?

Thanks ahead of time for your response.
-Rick