Reporting on UMs isn't just as simple as filling in a short message like on SAAFE.
The things you report for are- rape, theft, blackmail, assault, stalking. You get warnings about people being released from prison in your area.
A high percentage of the warnings come directly from police who liaise with workers. If you report something there are options to take things further. I have been given direct links to an officer after I posted something years ago.
It's not just something you go "Oh that guy was a bit annoying I think I'll make things tough for him" like people can do on SAAFE, it's used not just by workers to keep safe, but for gathering evidence in cases also.
I think if you read some of the warnings you'd realise that it is a very valuable tool that wouldn't be easy to abuse.