The ease of use, how much information you can get from it very quickly without having to spend hours reading through documentation or spending days talking to support staff is fantastic! I have been using redox for over 6 years now so there are not many things that I dislike about it (except maybe some minor UI changes).
If someone has never used any kind of EMR system before then this might be difficult at first but after getting familiarised with its functions will become easier than other systems out there. It's great if your organisation needs an integrated solution which allows easy access to all relevant medical records within one place as well as allowing users who need them to easily gain quick feedback regarding their current health status/problems etc.