I have, to date, never gotten the brand, not even when I sided with the Cult. My observation has been that the MC has more access to the minds of Minthara and Dror Ragzlin than vice versa. Dror Ragzlin aside, Minthara is a cleric with presumably a good wisdom and a trained mind - I don't think she really needed the tadpole to decide whether or not you're attracted to her, so there isn't much evidence she gets into your head with any depth at all - she recognizes when she's been probed past a certain point (a major improvement over Ragzlin), but she doesn't seem to get any other useful information. Is this asymmetry a result of the brand, or a result of whatever is so special you're the MC? Gale and Shadowheart are harder to "access" than Lae'zel and Wyll (I don't know the difficulties with Astarion as I never seem to progress much past getting him to admit he's a vampire) - this has me wondering if it's the brand, and whether people who get the brand so they can use cult magic items are setting themselves up for trouble when they meet higher ranking cultists at Moonrise Towers. Alternately Minthara isn't a very good cleric (she wears ring mail for heaven's sake?! Lae'zel's medium armor is superior in all respects, even cosmetically, so vanity can't even explain it) and it's just a question of strength of mind and training (in which case a wis 8 barbarian ought to have an interesting time on meeting future true souls).