I cut myself recently (until 2 months ago). I did try to see how deep I could go. Although I have no "values" to measure or compare how deep I actually got, it becomes FAR MORE painful the further you try to go.
As for using this as a method to CTB, I did my research on it. Statistics will tell you it will most likely fail. So naturally people will suggest a method with a much higher success rate or chance.
I did conduct research on this and looked for every possible information that might be useful. I believe that if you plan this correctly and have the necessary recourses (details which I will not disclose here), then this method can get you the desired outcome. It still won't prevent any of the physical pain, however.
And even then, other influeces are risking this method to fail. Like when you haven't bleed to death yet and get found, then that's it.