Pingdom's IPv6 monitoring was never practical on the free plan, because you had to forego IPv4 monitoring in order to use it. Granted, the right solution is to

Pingdom's IPv6 monitoring was never practical on the free plan, because you had to forego IPv4 monitoring in order to use it. Granted, the right solution is to make all checks dual-stack by default, instead of moving IPv6 to the paid tier.