I have both, but not much to compare besides both being Alliums. Very different looking plants. Blue Eddy is shorter with blue twisted foliage and less vibrant flower. I think it blooms later too. Both have been perfectly hardy for me in MN 4b and no fuss. Simply for the flower color I prefer Millennium, but the Blue Eddy foliage is a nice addition to the garden.

Blue Eddy is shorter

That's interesting as Millenium is already quite short...about 18" for me.

Right now, millennium has foliage to about 15" with goosenecked flowers to about 19".

Blue Eddy has foliage to about 8", with just the first signs of flowers still down in the foliage.

If you like the look of Blue Eddy but want something bigger look at Medusa.

If you like the look of Blue Eddy but want something bigger look at Medusa.

Thanks. I picked up both yesterday.

UPDATE (2 month later):

@pennlake(4 Minnesota), thank you again for the suggestion of Medusa.

It has been 2 months since I potted it and it has been in bloom for the past week or two. I like it very much, lots of flowers in its first year, and I may be wrong but it seem to be a more desirable allium for bees than the nearby in ground established Millenium.

UPDATE May 2021

I left Medusa in the above pictured pot and it easily survived this past winter (overwintered in the garage)

(I see that there is another of these late blooming alliums called "Lavender Bubbles"

https://www.waltersgardens.com/variety.php?ID=ALLLB )

Another good one. Been impressed so far.