A friend purchased a Miller tig welder, and hooked it up to his argon tank without a flow meter.  He has a gauge on the tank and set it for 20CFH, but I don't believe it was suppling the right flow of argon.  Can this be done without issues. Is a flow meter absolutely require to meter the gas evenly? 

Gauges and meters can lie. They either lose calibration, were never calibrated to begin with, or in the case of gas gauges, are set up for the wrong density to gas or gas mix. That being said, the right, high quality flow meter is worth it's weight in gold if you are going to do this a lot.

Certain shops test new welders by taping over the amp meters and flow meters, and have the applicants set the machine up by visual and audible feedback. If you actually have the field experience, it takes two minutes to get it dialed in.

If you don't know where you are going, anyplace you end up is OK. If you have a certain destination in mind, and have never been there yourself, maybe you need a map or a guide.

Thanks John for the info.  What I saw when we tested the welding machine, on aluminum, was dirty welds with lots of black junk on all the welds.  I personally did not like the welder.  It was a very basic tig welder, maybe a 175, with almost no adjustments except A/C or DC positions and a digital readout for the amps.  I thought the gas wasn't covering the torch and tungsten area enough to make an adequate atmosphere.    

Aluminum can be dirty to weld. I did a lot in my shop and castings were the worst. With aluminum you want to have it perfectly clean and wire brush or sand down through the natural anodize that forms on the surface. Also make sure your filler rod is clean and not dirty.  Nothing wrong with a basic machine. My Linde UCC-305 is a Hell of a welder and it doesn't have the new digital stuff or controls.

A proper flow gauge is worth the investment.  In the grand scheme of things, you will actually save money on several fronts in having one--from using too much gas (that junk adds up!) to wasted time with poor welds.

The dial gauges are about as accurate as sticking your finger in the air to judge the wind.  Sometimes that's good enough, sometimes not.

With Tig, it's also of benefit to change cups for different welds and tweaking gas flow accurately can give serious improvement there---for instance, a gas lens cup likes just the right amount of flow but gets turbulent with too much and can lose some benefit.

Also, a pinhole in the hose to the torch will cause all kinds of issues.

If the machine isn't high frequency tig your goin to have problems welding aluminum .

Make sure all your shielding gas connections are leak free. You can check with soapy water. I would not use a gas lense set up unless you or your friend are accomplished tig welders. Learn to tig correctly first. Gas lenses should enhance your work, not cover up crappy welds with bad techniques.