As Mark said, there are dozens of Key pad manufacturers but they are not protected and electronically controlled as Supra does. With Supra you can monitir and control who enters the place and how often agents have entered the place (with permission or not).
Furthermore, on a regular, manual dial, lock box, some agents call you to show the property, you give them the combo number and they send their customers visit the property on their own.
Be a professional and use Supra. It's a great investment.