I bought one of these a few months ago for the purpose of being able to detect "cloned" keys on Fords. This is important in my job, many Ford programming events require two unique keys and if one key is a clone of the other then the vehicle thinks they're the same key. I've found it very effective for that, you read both keys and see if the "Response" string matches or is different. A match means you have a clone.
Since then I have used it on a few jobs to check if a key was "dead". It works very well for this.
This is the usage I think would help most shops. You've got a vehicle that isn't recognizing a key. Is the problem the key or the car?
Zed Bull Mini is cheap, I paid $40 for mine. It's one of those tools you may only use once or twice a year, but being able to say "good key/bad key" in ten seconds and then move on is very worth the price.