Booker

Admin backend is solid and reliable.
Lots of options to customize. Too many at times since finding just the right setting can take 15-20 minutes or require a phone call to customer service.

Customer front end is weak and confusing. Booker does not allow certain booking options (CF2) to be used in iFrames. This forces you to send customers to a 3rd party website (not yours) to make appointments. Fixes and feature requests come slowly if at all.
If you are interested in using Booker be sure you know what you are getting into before you commit. It is very difficult to get 100, 500, or thousands of customers to move to a new appointment system if you later decide Booker is not what you expected. Get used to what Booker looks like now and be okay with that for the long haul. Don't plan on being able to add a feature of even getting Booker to fix bugs. Booker will show you a long list of "fixes" and revision numbers of updated software. I have never known any of these updates to address a bug of concern we had with the SaaS. Customer requests are ignored and bugs are described as features. Yes, they really are! For example, in some places staff names are sorted by first name and in other places they are sorted by last name. This does make it feel like you are using different software products and will infuriate you at times.
Different interfaces all work differently. In other words, they all feel like different products. We use the admin interface, the Booker iOS app, the Booker customer app, CF1, and Facebook app. That seems like lots of great options until you realize how disjointed and different they all are. You are not merely learning one software package, you really have to learn them all.