There is no danger from using the test light, the battery is disconnected from the car during testing, the only load is the test light. I use the test light cause I can easily see it from the interior of the car as I'm pulling fuses. Any drain that will kill a battery in a few days will light the light even if its dim. In most modern cars, there will always be a slight drain from devices that needs electrical power for memory. This can be seen with a multimeter but this drain is expected and is usually and most likely not your problem.
I don't want to be mis-understood, I'm not saying a test light is better but unless you are an electrician, most people have never used a multimeter let alone set one up properly to read amps and then you would have to interpret the data to determine if you had a problem or not. The test light is either on or off. if the test light lights, you have a problem if not you don't. In 30 plus years of working on cars, this method has never failed me yet.
Mark