Cool,
My instructor actually told me about this technique. His shins are like steel. I did it for a while and like you said. They would be sore, but not bruised. Bruised shins take about a year to heal, at least it seems that way. Nothing like a huge knot on your shin to make you work on your hand techniques and kicking with your weak let...
I used an escrima sitck and just tapped them, up and down, while watching TV. Right now I have one shin that feels no pain and one that DOES!!!!
Keep the training up and kicks low,
jbkenpo