Honestly, what I like best is the customer service. Whenever I need help, I get a real answer. It doesn't mater whether it's by phone, email, or the helpdesk. I get a quick, accurate, useful response. Zen Planner is committed to improving their product regularly, and they care about what their customers think. Obviously, I can't always get EXACTLY what I want, but when the product doesn't work they why expected, my account manager helps me understand how to work within the way the system is designed, and on occassion has helped streamline my business processes as a result.
The new staff app is awesome for taking attendance quickly, too. Looking forward to seeing how that grows.
I think that the appointment scheduling calendar could have a better interface both for the instructors and the users. There's a lot of redundant navigation when people want to book multiple appointments. However, I believe that an upgrade to the calendar is underway and coming soon.
I recommend Zen Planner to other martial arts schools all the time. I don't think there's another product out there that can do more or do it better, and I know none of them can beat ZP's customer service.
We use Zen Planner for most of the student management tasks of our business: track and collect payments for memberships (including auto-pay and auto-renew). Track rank progression, attendance, and class assignments. We allow students to register for special events and private lessons online as well. By 2017, we also plan to use the online store for our retail needs.