THB,

You're quite correct.  Renting or leasing the larger oxygen cylinders is a smart move with a good bang for the buck ratio.  That's exactly what I do... or did.  My requirement for the M60 was for a 23 lb oxygen cylinder no taller than an E-size oxygen cylinder I could carry to and from the car as a "roadie" for local travel and work. 

I get (or got) 10 to 12 aborts from the M60 it vs. the 3 to 4 for an E-size oxygen cylinder that rents for three times what it cost me to fill the M60 from a larger M-size cylinder.  That also simplified the regulator requirements as both the M60 and larger M have the same CGA-540 fill fittings. 

Besides that, even though I'm feeling younger every day on the anti-inflammatory regimen of Omega 3 Fsh Oil and vitamin D3 I think is responsible for my remission for CH, at my age packing around a 73 lb cast iron M-size cylinder for local travel was a bit much and the K-size, out of the question.

Take care,

V/R, Batch

Top of the line oxygen regulators have Inlet Filters. The Flotec InGage™ regulator has a 10 Micron Sintered Bronze Filter on the inlet and a 30 Micron Sintered Copper-Nickel filter in the flow orifice assembly.

In the "for what it's worth" category, the average human hair is 70 Microns so these filters sound great at first blush. 

Having said that, the average bacteria is 3 Microns, lead dust or mercury aerosol from a broken CFL light are 2 Microns, and 90% of all oil aerosols associated with high pressure gas are 0.5 - 2 Microns.

Putting all this in perspective, the odds are you'll inhale far more pathogens and particulate contaminants walking down most city streets or riding in public transportation in one hour than you would inhale from a hundred welder's O2 cylinders.

Take care,

V/R, Batch