In my experience, aftermarket key fobs work just as well as official key fobs. However, the quality may not be as good. For a spare key, this doesn't matter. But for long-term use, you may find that the buttons wear out quicker than an official factory key fob. In an emergency, though, you'll be glad to have a couple of spare key fobs lying around, and the durability doesn't matter if you need to use them occasionally.