The ease of use, no coding required for development is great! Also they are very responsive when it comes time to implement changes or enhancements that we need from them as customers/clients (we're an online bank).
I wish there was more integration between their mobile apps vs just web-based access which can be confusing at times but overall its been pretty good so far. We have used this product in conjunction with other software solutions such as Xero & Sage Payroll - all integrated together via one account management portal allowing us to provide seamless service across multiple channels within businesses including B2B clients etc.