I've used my Harbor Freight compression tester several times. It works well, and is cheap. If you're going to use it a bunch I'd buy a good one. If you're only using it once in a while the HF tester will work. Make sure you get a Diesel Compression Tester not a Gas one.

Cold verses Hot - To me it depends on what you're troubleshooting. If you're having hard starts. Then cold compression will tell you what the engine is working with when you try to start it. If you've got rough idle or lots of smoke then hot compression might tell you why. High cold compression is only going to go up when the engine is hot.

__________________