The Janine card is a middling card in terms of value its more valuable than most Supporters in Night Wanderer, but its not quite top of the list
Blood Servitor can be played in any deck to help you create a Blood Token
For instance, most of the Mekk-Knight monsters have this as their first effect: If 2 or more cards are in the same column, you can Special Summon this card (from your hand) in that column This means that if your opponent has a spell and a monster in the same column on the field, you could special summon a Mekk-Knight to that same column in the monsters zone on your side of the field
The fact that it has Flashback is what really takes it over the top for me, as it forces opponents to play around it while giving you the option to ramp more if needed
Since you have to play the exiled cards this turn, playing this in the late game will ensure that you get full value out of it
While having to exert to use an ability is usually not great, this exert ability will grant you more lore than questing would