optoutprescreen.com How many have used this?

I was looking to opt out of the prescreen mailers from the 3 credit reporting website, when I researched from transunion website on how to optout they have a link for this www.optoutprescreen.com.

Even though I trust transunion, i am not 100% sure about optoutprescreen.com.

Has anyone used the forms or electronic optout provided by this website?