You get what you pay for when it comes to tools and being a professional mechanic for the last 30 years I can vouch for the fact that Snap On does make some of the best tools out there, no question. Harbor Freight is good for the once and a while mechanic or hobbyist that will only use the tools a few times. If you buy from HF, just don't expect the tool to last and or be accurate. I would never, ever, consider buying a torque wrench from them.

Back to the topic, buy one of those adapters shown above for a couple bucks and you can use any compressor.