I own the Alkin W31 manual version. It is all you need. It fills so fast that the auto drain is only ever used when filling a 6.8 or 9 liter tank from zero. How often do you do that? Once a year or less? A refill from 3K psi will take 5-8 minutes depending upon the tank size. It only requires the lines to be purged after the fill is complete. I set my phone's alarm for every 12 minutes when I fill a tank from zero and purge once or twice at most. As far as the auto shutoff, it isn't a necessity either. The compressor has a pressure relief valve set at 4500 psi. If you aren't monitoring your fill and the compressor reaches 4500 psi it will vent the excess pressure until you stop the compressor.
On slower filling compressors these two features are desirable if you don't wish to sit through a 45 minute or longer fill. But on the W31, the extra cost of these features is kind of an unnecessary luxury since it fills so fast. Save your money. The manual version is the way to go for the occasional user like most of us.
