Unfortunately the dataset performance is really slow and becomes almost useless when response time is 20-40 seconds when interacting with the reports.
I hope this is on the top of the agenda for the development team since these kind of auditing is highly requested for many customers and can add a high value when justifying investments into Power BI in the organization.
Improving the performance of the usage metrics reports is at the top of our priority. Work is in-progress which should significantly improve performance. We should have an update by end of September or October - stay tuned.
Separately - unfortunately there are no current plans to add email subscriptions to usage metrics, though I would encourage you to create/vote on the idea at ideas.powerbi.com
I've noticed that using the ViewsCount measure seems to cause most of my slow downs. I am connecting to a report usage metrics dataset on one of my workspaces through Excel and finding that almost any time I pull ViewsCount into the pivot the refresh never completes. I've waited more than 10 minutes at this point and its still trying to bring in the results.