Hello,
I may have found a good monitoring tool for any servers (Raspberry Pi, virtual servers and more) that is free and open source.
You only need to install an agent on the server you want to monitor and all the metrics are available on netdata cloud.
They have added a python script to get tor traffic read and written and show it in a graph.
I didn’t find any cons and it seems very easy to use compared to Grafana, Prometheus, tormon and others. For the safety, do I have to take into account some criteria to avoid problems?
I mean on security and confidentiality wises. How do I know if this tool is safe to use for Tor ?
If this tool is safe, it would be nice maybe to improve the tor python plugin to get more statistics like number of unique clients for bridges, countries, flags and more. Im not very good in Python unfortunately so if someone wants to help 
Thanks 