Curious about other's thoughts on "splashing" Blood - particularly on a nation with no Blood access on its recruitable mages, but who manages to find slave pits (or similar, like the Lower Throne), so they've got a meager (but steady) income of slaves coming in.
Worth the time and expense of researching blood (how far up the tree?) and training up one (several?) caster(s)? Blood hunter(s)?
It can be quite useful sometimes. (Although only 2 come to mind...) Note that if you empower a commander for slave hunting duty (and slave hunting duty ONLY), it's probably worth it to do so to a normal commander, to save on upkeep. They're more likely to survive stray arrows too!
Like if you have native earth magic (for Bloodstones)
A Communion focused nation can also get decent mileage out of Rejuvenation (AKA, kill slave, reset fatigue for caster+all slaves)
There's almost certainly more good cases where you can get some benefit from splashing, but I highly doubt you'll get much good out of just straight blood, it'll take far too long to bootstrap a blood economy to really leverage blood magic. Figure out what you can potentially do with it, see if you can fill in a gap or amplify your strengths. And remember, it's there to support your nations bread and butter, not stand on its own!
(P.S. I've never played a blood nation. Bootstrapped into it once myself though, but you REALLY need the Lower Throne or a province that lets you recruit Blood mages (like the ever elusive Garnet Amazons) to do so... Or you could trade I guess.)