This filter does the job perfectly if you use it in the correct manner. A lot of people here are just using it wrong.
A. This is not a replacement for a larger "main" in-line water/oil separator. IE a 1/2, or 3/8 filter like; http://www.amazon.com/Ingersoll-P39344-600-VS-2-Inch-Filter-Regulator-Piggyback/dp/B0057D8MCI/ref=pd_cp_hi_1 This unit is meant to be used at the input end of a paint spray gun, hence the low pressure. It not intended to run at 90+ PSI for something like an impact wrench or air hammer.
B. You can't hang this (or any water separator) right off your compressor and expect it to fill up with water. You need to provide room for the compressed air to condense the water out. IE 30+ feet of hose or pipe. I guarantee you if you don't see water after heavy use of your compressor move it to the end of a 50 foot hose and you will be draining it like a colonic bag!
C. Yes it's plastic. Would you rather have glass that would explode like a grenade the first time you drop it on the shop floor with it cranked up to 120psi?
D. The drain is on the bottom for a reason. See point A, its meant to be used while mounted at the end of a tool like a sprayer that remains upright. Not mounted on a hose that will lay on the floor.
I have mine at my spray gun behind 60 feet of plumbing and 2 other larger dedicated 3/8" water separators and it still collects a lot of water.