It can be dangerous to fill your own tanks, if you don't take proper precautions. If you do, then the risk can be greatly reduced.
I know of several folks on this site and on talkglass have their own tank fill systems. Here is the play by play on my system.
http://www.talkglass.com/forum/showt...light=homefill
Many folks on this site immediately think it is too dangerous, and for them that is probably true. But if the system is well designed, properly spec'd, and properly operated, it would be the same as a welding supply company filling K tanks for their customers, except that you would bypass the welding shop and avoid transporting 2000 psi tanks in your vehicle.
Many folks here have no issues with having K tanks (or propane tanks) inside their garage near their torch station, but would never fill their own tanks. But if you think about it, the only difference between the K-tank user and the K-tank filler is basically a smal length of high pressure hose linked to a compressor between the tank and regulator. That is it. So in my mind, the user of the oxygen tank is taking almost the same risk as the filler of an oxygen tank. That being said, if you are serious about filling your own tanks, make sure that you have researched it to your satisfaction and understand what you are doing.