The fact of having an open source software in one place makes it easy for everyone with development background or willing learn quickly! I would like more customization options such as configurable workflows & rules but this can be done easily if you have developer skills :) Currently we use flexrule's Rule Engine for our B2B eCommerce site which helps us keep track of all product orders placed online (eBay marketplace). The best part about this software is its flexibility in terms of customization. It allows you to make rules for any kind of scenarios which can be very helpful when it comes to automating many tasks. I have not found anything negative so far. You should definitely give it a try if you want an automated solution for all kinds of problems. We use flex rule to automate our processes related to billing and invoicing.