Metal filter bowls, or metal shrouded air filter bowls are available from a host of compressed air component distributors.
Many manufacturers offer metal clad or metal bowls as options only, with their main filter or lubricator lines having polycarbonate type filter bowls without any metal guarding or over-bowl-shroud.
The polycarbonate bowl offers an advantage in that you can see through the sides to the inside of the bowl. This is quite important if your filter bowl has a manual drain. Your maintenance operator needs to make sure that the level of contaminant in the bowl, the water and sludge that the filter will remove from the air stream, stays below the bowl separator and in the quiet-zone at the bottom of the bowl. Being able to see the level allows the operator to manually drain the bowl as and when needed.
Here is information about the components in a typical filter bowl, if you have interest.
However, do check the specs on your filter unit. You have to be absolutely sure that the filter is rated for the pressure it will see in your application, particularly if your compressed air discharge pressure is over 100 PSI.
If you are running an air system where the pressure may exceed thae level that a polycarbonate bowl is rated for, you will want to select a metal bowl, even if it means going to a different manufacturer than the one you presently use.
If you decide that a metal filter bowl is right for your compressed air application, I recommend that you get one with a sight-glass so that you can tell if water is building up in the bowl, since metal is opaque and you will not be able to tell what the water / debris level is otherwise.
Even with an auto-drain on the bowl, having the site glass means your operator will be able to diagnose a drain blockage quickly, and clear the problem before the crud-soup coming down the air line plugs your filter element completely.
That same oil has a reputation for being detrimental to some polycarbonate filter bowls, hazing the interiors and ultimately degrading them to the point of cracking and creating the potential for a catastrophic bowl failure.
If you have oil carryover into your compressed air, and do not have a coalescent filter upstream to remove the compressor oil, that oil may damage the polycarbonate, and you would be better off selecting a metal or metal shrouded bowl.
If it were up to me, and there were no over-riding reasons why I should not, I would always select a metal bowl for my air filters. Be aware that some mini-filters may not be available with a metal bowl option at all.
In getting compressed air to your application, "it is better to use a longer and larger diameter air hose than an (electrical) extension cord" for your portable compressor!