I started with the free booking calendar and wanted to have more control of the form fields and the ability to edit reservations so I decided to purchase the Business Small version. This was the most expensive plug in I have ever purchased and I don't regret it for a second. You get what you pay for - and this not only allows booking on my website, it provides me with a great database and easy managing of the reservations when I am logged into my site.
OK, here is the MOST IMPORTANT part of this review - I had a problem when I added SSL to my site. I contacted support and got an immediate response. When I was unable to fix it myself (problem was a little more complex), I gave them a temporary admin password and support worked HOURS troubleshooting and fixing the bug for me. Turns out, it was not booking calendar, but a conflict with another plugin I was using. Instead of just telling me the plug-in was causing the problem and walking away - support actually REWROTE code on their product to make it work with my plug in. Now that is great support!