I use igloohome key lock system, it's great and I love the convenience!
I initially had some issues unlocking the box, but customer service responded to my inquiries very quickly and worked me until all questions and concerns were resolved. I think this is a genius pairing with Airbnb to create an easy access system for the hosts and guests. Especially the communication between igloohome and my arriving guests, it takes away the burden of watching the clock.
I'm sure there will continue to be improvements and new technology coming forth, but this system and my customer service representative (Matthew) have been wonderful so far! I can't wait to see what they come up with next.