Well...I can say that I have been lucky enough to have gotten head from 2 different ladies with tongue studs....I must say, it's all in the way that you use it....one girl's head was very good (and you could feel the stud and it made a difference)....and the other girl you couldn't tell she even had one.
It does come down to skill....but I think, if the stud is used properly, it can "add" to the skill.
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Got under the monkey's skin like no poster ever has...I WIN!!!