We have witnessed ROI. It is worth the money. 

We have seen a return on investment over the past four years. We can be assured of the perimeter security system's stability and ability to sustain itself in good conditions.

We have seen a return on investment. Teams are being hired and staffed to meet the demand of having Fortinet implemented on our client projects.

We have seen a return on investment in the form of time saved and increased customer satisfaction.

I avoid this question with security tools as there is no real return on this, just a lowered burden to manage risk. I will say the tool requires maybe 2 hours of actual focus a week, so much less noise than other tools. enSilo also reduces our risk more than any other tool we have (firewall, web filter, email filter, etc.). From that perspective, we get the most risk reduction with the least burden from enSilo.