Dr. Numb is just a generic topical anesthetic cream. It is neither the best nor the worst stuff out there but having had topical anesthetics used in operations I would say that it is only effective for around 40 mins max anyhow and can take a couple of hours to take effect.
Also the pain kicks in as soon as it wears off anyhow as you have no endorphin build up.
It is really something you would have to test for yourself as to how effective it is.
Tattoo pain is bearable and nobody will laugh if you do grit your teeth, swear, cry or pass out as long as you sit still!
Tattoos hurt and I am currently cursing my way through the after effects of my fourth sitting on my back we did 3 hours with no break and by that time I was ready to start really cursing.
The only difference between a person with tattoos, and a person without is this. The person with tattoos does not care if you do not have any.