We have installed OpenEMR in a medium size clinic, in the province of Chubut, Argentina, in September 2016. So far, 7 months later, there are 100 registered users and almost 10,000 patients. There were no problems so far.
The administration asked us for some reports, beyond those programmed in the OpenEMER system. For example, a list of patients without health insurance. We solved it with a customized MySQL query.
A Gynecology form was implemented with some standard questions.