I love Timetrade for the way it integrates into Outlook. I often do projects where I need to do a lot of interviews, so I can set it up so that when I send out invitations I don't need any back and forth on email to set up an appointment. I just add the custom link into my email and the interviewees choose their own time using parameters I set for my own convenience.
Be sure to do a couple of things:
1. Set the end date beyond which you rather not have meetings booked. Meetings booked by strangers more than a month out often don't happen.
2. Make sure you pro-actively block out your calendar for times you want to keep for yourself, staff meetings, impromptu client calls, etc.
3. Keep meeting times short (i.e. 30 minutes) and in the messaging indicate they should mention it if they think they need more. That way you don't block out time unnecessarily.