My Girlfriens and i have a bit gag, its my favorite, its all rubber, the bit is just under or is an inch thick with a strong strap, evan tight there bearable and look incredably sexy. i dont know about metal ones though, neaver tried a metal one, i guess a metal one is what she is after sounds a little unforgiving to me, id suggest getting a rubber one first, as a training type thing.

oh and what do you class as a normal gag, because id class Bit gags as reasonably normal there not fancy but they work wonderes expecially whan they are tight.