A self-inking stamp is a rubber stamp mechanism that contains a spring, stamp and a pad. The stamp rests on the pad when it’s not being used. This way when you want use the stamp it is ready to go. When the stamp is resting on the stamp pad all the time with pressure, it causes a couple of problems. First, it places an impression (indentation) in the pad, if you want to put another stamp on your self-inking stamp it is advisable to change the pad also. If the pad is not replaced your stamp may not work correctly. Second, the pad over time will wear out. I suppose this isn’t really a problem. That happens to every stamp pad eventually.
Ask people you know, they will certainly tell you what they like or don’t like about thier stamps. The better self inking stamps are made of an ABS plastic and are very durable. The “no-name” brands you see in ads in the sunday paper are made of a less expensive plastic and are not as durable. You may also find it difficult to find replacement pads for off brand stamps as well.