Passionless sex [between any genders] is a chore to slog through. Though, in all likelihood, your customers haven't seen thousands of pornos, so they're probably more forgiving. Nevertheless, FMTBB is hardly a formidable specialty piece - for the usual reasons.
In addition to mechanical encounters, these Brazilian T's just can't work it out on a consistent basis. Some get aroused during foreplay ... but dangle during penetration, masturbating uselessly after the fact. Others never even get that far. However Sabrina - the least passable of all - manages to maintain mighty wood and blow an appreciable load. (At least her partner appreciates it; the sight of expended jizz on her belly makes him toss his own special sauce.)
Retailing: Tranny filler.