The Luger pistol is a poor choice for self defense.
The pistol was designed before modern JHP rounds were invented which means it is likely to not feed those loads reliably.
Even with FMJ loads, which should NOT be used for defense, I would not consider the Luger design to be reliable enough for defensive use, except in a dire emergency.
Reliability aside, the trigger on the examples I've fired ranges from "Pretty Nice" to "Downright Awful" and the sights are too tiny for easy use. Don't forget any example you find is going to be at least 50 years old (except for a few later commercial repro runs) and may not be in the best functional shape.
The Luger is an interesting collectable, but should be relagated to a range toy.
If you are serious about selecting a firearm for self defense, as you should be, there are many much, much, better choices then a Luger.