SAP MII is great at what it's meant to do. It provides insight into the industrial IoT data being generated by a plant/factory and can even provide intelligent analysis as well. However, it is a bit niche and really only needs to be implemented if your use case requires those specific services.
If a proper UI5-based implementation is done, the system works at best if a proper application server and database exist. However, from a customization perspective and an easy-to-implement application-from-scratch perspective, MII is top-notch compared to the other mentioned systems. SAP ME sits on top of SAP MII as a foundation.
Documentation on some of our implementations was lacking. As an example, creating the query that reads the tag is explained through the documentation but this only explains very specific data models. Other models are not explained and take time to debug. Customer support was willing to help and an official note was created after we found some issues with the integration tools.
SAP MII is a robust platform for data visualization and data integration. It isn't very intuitive and has the shortcomings explained throughout the review. It still uses old Java versions which is incompatible with updated versions. The SAP ME and SAP CP provide cloud-based solutions that seem to provide a more innovative approach.
