I dont know if its All Master Caster's items, or just these.. but, me and my wife (Liliah, mnk73) where out, playing with are Summons, (me Rdm/smn, her mnk/smn) and had these on.. with them on, her Carby was only dropping 1mp per tick, with her Spirits dropping 2. With me, it was Carby 3, spirits 6. We did this with and without refresh (she got MP BACK with carby out) and with differnt Items on, her switching to my Dark staff, and back.. and it was very clear.
So, if anyone knows Why this is, let me know:)
Im going to try to get her to sub whm and see the effect on the MP cost of spells.. Hope this helps someone.