actually the conjuring guy sells those tomes

they mean the permanent variety, not the casual 60 seconds guys
master spells quests, college of winterhold ....
IMO the equivalent of spellmaking in more fancy
(then why are people say 2 dremora lords? people confuse me this svcks.)
60 second dremora summon variety. ordinary spells. you can summon 2 at once. good for close combat.
a thrall is a permanent summon that come from the master spells quests
anyway, I m not that far yet
one thing I wish is that bethesda added some stealth summon in a future patch,
because nothing svck more than your falme attronach shouting *look here bad guy, we re ready ... come and get us ...*
when I m tryting hard to stay undetected
which remind me only 2 companions are stealth, and not that good at it (jenessa and faedal)
and the dog isnt even stealth, or disciplined for that matter (weird for a wardog)