[Soyweiser]

My small tests and experience seems to imply that a SDR counts as an additional B level for both the find chance and the amount of slaves you get. Mine are also guesstimates. But they all increase the power of your bloodhunting. And even if they provide one additional slave each turn on a b3+ mage, that is still free slaves after turn 5. (Not totally true of course, as you waste one turn creating the SDR). This increases micro as you never ever send out a hunter without a SDR.

But as I said before, I'm not totally convinced SDR removal is a good idea. (Boosting some nations with a douse bonus for example just moves the issue around a bit (disregarding the additional mage turns and the used misc slot).

Ps: you get forge bonuses on blood items, just not the contracts, the black heart, the other blood heart, and probably one other item.