Aggregate availability from multiple calendars

I'm constantly baffled that MSFT hasn't addressed this issue, it's not that hard and will make the Bookings product actually useable! Here is my FREE Calendly hack for this in case it helps anyone else in the future:

1. Setup a Google Calendar account you can use to just for calendar syncing. (e.g. mycalendarsync at gmail dot com).
2. Go to your online Outlook account and click 'Share' on the calendar you want to sync, and then put in the Gmail address you just created. You will get a link to then go to your new Google calendar and then add new 'Other' calendar as web subscription.
3. Setup a free Calendly account using your normal calendar/email.
4. In the Calendar Sync section, add the sync Google calendar you created earlier, then in 'Check for conflicts' hit Edit and choose those subscribed calendars from your new google calendar.

Not sure how scalable this is but it works for the 4-5 calendars I'm trying to sync and provides me a share URL I can use for my clients.