Before any hosts consider installed key safes or keyless entry technology etc. they need to look into their home insurance policy because quite often these will invalidate this.
A recent guest broke my front door lock, which was very secure and very expensive, so I had lengthy converstions with the locksmith about my options and he made it clear that most insurance policies in the UK require a British Standard lock and often that you deadbolt the door at night etc. I had asked him about getting a keyless entry system but he warned me to carefully check my insurance policy before doing that. I don't know about lock boxes, but I would imagine there is a similar issue there.
Most UK insurers don't cover you if you are hosting Airbnb guests anyway, but I imagine those that do have even stricter restrictions about entry systems. I would be interested to hear from anyone who uses one of these and knows.