Uptime % has the benefit that it's easy to understand.

I don't think this is true - people struggle with exponentials. Most people can't intuitively grasp the staggering differences between 2 nines, 4 nines, and 6 nines of availability.

	▲	charcircuit 22 minutes ago \| parent [-]
		Why should the customer care about how hard 6 nines of availability is? That's the company's problem, and not the customer. If you want to make it more friendly you could just say "10 minutes downtime this week" instead of a percentage.