Review on Supco M500 Insulation Tester: Reliable Megohmmeter for Accurate Measurements, Includes Soft Carrying Case, 0 to 1000 Megohms by John Talcott

Excellent value for money. I work in a commercial industrial air conditioner and regularly disassemble engines. This thing is pretty accurate, I tested it with a $1500 AEMC device and it worked fine. I would not recommend it for cars over 25 hp. It's just not accurate enough for trending. However, for small compressors, fan motors, etc., this works great. It's also good for checking wiring in devices for those "intermittent" electrical problems we love to run into. The downside is that the cables are too short.