The service unit enacts the Count Me reporting implemented as a hidden command in rpm-ostree.
The timer unit triggers Count Me reporting weekly at a random time. Disabling or masking this unit effectively disables Count Me reporting, regardless of the setting in RPM repository configuration files. See systemd.timer(5) for more information on how to control systemd timers.
The man page rpm-ostree-countme.timer(8) is an alias of rpm-ostree-countme.service(8).