We use them by leaving them in public bathrooms or by handing them out at halloween.
No doubt some people are offended by the direct confrontation with the Gospel reality. After a halloween when we gave them out along with candy, I had an angry parent come to visit me. He asked "Did you give this to my child?". I said yes I probably did. He said "These are not age appropriate. I go to church too but these are not age appropriate". I said ok, thank you, we have some for younger kids. When our kids passed them out they might have given the ones that are for older kids to the younger kids. He said, This is not what halloween is all about! (I wondered what is halloween all about but just listened patiently). The next year we made sure to give the ones for younger kids to younger kids and the older ones to older kids. I wonder if the parent was concerned about the scary scenes depicted, or if he was convicted himself as he read it. I compared the scary scenes depicted to the halloween costumes and other saturday cartoons or typical movies kids see and thought, this is pretty innocuous.
The Pharasees were also offended, but some, even some believed.
Some people who come from a rough background of drugs, poverty, and family dysfunction, might more quickly recognize their needs and relate to the tracts that often portray these types of behaviors very honestly and openly. The tracts are loaded with Scripture, which is what has the power to change lives.
Others who think they have good works, live in the nice suburbs, have it made, etc, might seem more likely to come to Christ through close relationships with Christians who give their simple testimony, and share scripture, which again is what has the power to change hearts, as God's gives grace.
Either way its God's Word that does the powerful work on hearts and as God gives grace.