Kind of both for us.
Yes we do. But we also use it for in house backups.
In our business we sell "Backupstations" (small PCs with a RDX Bay) with Veeam B&R + Veeam ONE, which also acts as a Veeam Repository.
If the customer wishes so, he can login to Veeam ONE a check status, but most of the time we do this for them. So, we use both, the email notifications from Veeam B&R which backups the servers, and Veeam ONE. So it would be really handy, to check the endpoint backups via Veeam ONE.