Well, the Taste Temptations mattene is described as "vivid purple" and the Strength lipstick is in the book as "bright violet". Mattenes are usually sort of a creamy matte, while the one in Strength will most likely be one of the new mattes, which ought to be not too drying, but won't be quite as moist as a mattene.
My MA seemed to recall the mattene as being rather close to Potent Fig, but I'm assuming it will be a little lighter than that one. The Strength one is close to Heroine (how close, it's hard to know, but it's not particularly bluish).
Unless the mattene is exactly like Potent Fig (which I love and have a BU of), I'll probably get both, d'oh.
Oh, one last thing about dark mattenes - they tend to be a little fussy to apply. The lipstick will definitely be easier in that department and will have a little better staying power when worn.