I made deep research if any of free network monitoring tools supports Netflow. No success, or no luck ;-) . Luckely I have friend - developer which developed app with multiple funcitonalities named Grafolean. I ask him if it is possible to implement Netflow functionality in Grafolean and YESSSS, he did it and it works great. If anybody is interested, please try. Grafolean is FREE for use and it will stay FREE! If you find any issue or you stuck somewhere ask question on github, developer is very responsive. More details and how to install you can find on https://github.com/grafolean/grafolean
Here is short video how to implement Netflow in Grafolean https://youtu.be/5p32cFvvQ5A
I Hope you will find this app usefull. I did it, and it solve my problems when I need to find who is heavy user or which device "produce" strange traffic in my network.
Examples from my Grafolean: