When you buy self defense weapons you must not get carried away with propaganda published by the sellers. There are no weapons that work all the time alike. You must expect failures. Therefore, you need to have your back up plans. When you purchase your weapon, there are many things you need to consider.
One of the important facets of buying your weapon is to consider the local regulations. All the weapons are not permitted everywhere. Therefore, you need to learn the local regulations that affect their use. Just to learn if a particular weapon is allowed or not, you could ask the local police.
If your weapon has an expiry date, look at it before you are going to take it along with you. If it is one that works on batteries, check if the batteries have the right level of power to operate it effectively. These are some of the basic rules to follow when you are using weapons for self defense.