I got one of the cheap ones and I don't have any complaints. It is just for light use. I am not a mechanic and I'm not rebuilding a Volt or anything like that.
If this is for monitoring and you will use it frequently, the one thing I would recommend is to get a unit with a physical on/off switch on it. I understand if you leave one plugged in while the car is off, it does not power down and puts a drain on the 12V battery. Not something I would want. Being able to turn it on/off without plugging and unplugging it is a convenience.
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