I thought I would share my experience using G3 Scratch Removal cream. The scratch or should I say large deep scuff was deep enough to feel with your nail and about as large as your thumbnail on my rear bumper. It did not damage the paint coat, just the top coat. I bought some G3 scratch remover and G3 Waffle Pad.
To apply I found I had to carry out the advised method of application several times (rubbing the cream over the scratch area), using as a result way more cream than recommended. However to my suprise it has completely removed the deep scuff/scratch... But also I found it also manage to start to remove the paint from the edge of my bumper due to the back and forth motion advised for application. Luckily I managed to notice the paint on the edge in time before it got too bad.
I was sceptical of scratch remover creams, but I can confidently say it does work with a bit of elbow grease, just be sure to frequently check the area you apply the cream incase like my experience after some time of rubbing the cream in to the scratch area you may also be rubbing the paint thin on edges of the body work near by.