I play a character with similar abilities in a LARP (I get to ask OOC questions of characters regarding their motivations, abilities, etc). It's part Batman, part Mentat, where you have an insight that Others Just Can't Get. Like "This is probably the best place the enemy would put reserve forces to ambush you" or "There are actually two groups opposing you".How do you want to run Polesius' probability trance ability? It seems distinct from divination spells, which ask an ineffable godling for information that may be deliberately withheld or simply miscommunicated. The trance gives me "useful information regarding a question concerning a specific goal, event, or activity" by weighing probabilities and existing information.
I guess I see it kind of like a human computer or really smart guy drawing logical conclusions. Maybe the difference is that when it fails, the user basically knows "I don't have enough info?" Anyway, it's a 1/day ability, so I may as well see what it tells me about going downstream to this small town.