The blood hunting without patrolling things really puzzles me. So pros, you don't have to acquire a patrolling force and pay upkeep, you don't have to occasionally move when your population drops below 4000. Cons you lose income, you lose blood income, and if you're lazy like me you lost the ability to recruit mages in the blood hunting province (building a lab is a small price to pay for not having to aggressively micro)
Seems like from a cost efficiency basis it makes sense to at least keep an army of patrollers who's upkeep is less than the value of the province. From a blood hunting efficiency point of view once your unrest is 100 the straight chance of failure is 25% according to the manual. That means for every four bloodhunters you are paying one to just make people angry, and without managing unrest you can get to a hundred unrest in three or four turns, seeing as the unrest generated by succeeding at blood hunting is 1-(3xthe number of blood slaves collected+4) it would take on average 132 blood slaves collected before the chance of failing a blood hunt in that province is 50% from unrest alone and 265 blood slaves before blood hunting was entirely shut down by unrest. Now this is assuming that the passive things that reduce unrest balance unrest caused by failed blood hunting. This becomes less and less true as unrest rises because it causes more failed blood hunting.
For much of the game I only had one or two B1 blood hunters per province (it seemed to work best with just one), although they were effectively B2s due to the xibalban blood hunting bonus, which meant there'd be less unrest without slaves. As a result, PD plus Order 3 were sufficient to keep unrest fairly low.
Unrest only became a problem when I started farming provinces with significantly more hunters to increase my blood income, which increased it rapidly in the short term, but then started to decrease it again as unrest rose. I could have raised armies to patrol, yes. I didn't because I was spending the gold on more important things and didn't really need additional slaves that badly - and taking more territory was providing me with new places to farm anyways.
The province with the highest unrest (and the most blood hunters) at the end of that game had 271 unrest, and 13 blood hunters (half of them effective B3s with 100% level checks, the rest effective B2s with 90% level checks, because ea xibalba) - but that was the result of me taking all blood mages off of research after I finished researching every research topic in the game.
That was a very abnormal game, though. It was a fairly large map, with 5 players, and the throne settings were set to make it a long game. The player right next to me was EA Pangaea with a double water+fire bless, and they took two forts of mine with super-centaurs, but then said that they couldn't remember what they were planning to do, and went AI. The AI proved inept and didn't really properly use or even produce the super-centaurs. If they'd invaded me before I had mass demon summoning instead of going AI I'd probably have been screwed. In the end I dom-killed everyone with blood sac, but also had enough slaves for demon knight + storm demon armies.
I'll note that in my first attempt at ea xibalba I tried blood hunting my capital, and patrolling to keep unrest down, and it decimated my population and gold income despite controlling unrest, which is why the second time I played them I (a) didn't blood hunt my capital, and (b) didn't patrol.