I like the front cover of the premium box, and love the spine, but am also unsure of the back motoslave design.
I feel that the strongest designs of the premium sleeves are the ones of Nene, Linna solo, and then the first one of Priss. I wish that maybe Nene's could be transferred to the final volume, so that I could utilize all three designs. Nene's best episode is the final one anyway, so it'd make sense to relocate her to that cover. Not really fond of the Sylia one as it's an awkward pose, and I agree that Linna vs. the boomer is a little out of place in regards to the other designs.
In terms of the coin, I feel that Priss' image is absolutely terrible. It's hard to tell that she's even female in that design, and the odd nature of the helmet as part of the image creates a visual illusion where it looks like she has large dark manly eyebrows. It's an incredibly unappealing image, and I wish an alternate design could be made to work. Especially now that you're increasing the size of the coins for premium backers (or for everyone? I forget).