HarperOne meant by "non-flex imitation leather" has been answered. It is similar to what Baronius Press has done with its Knox Bible, a hardback edition which is covered in (bonded) leather. In this case, however, HarperOne has simply used imitation leather, which I greatly disliked in the flexible imitation leather edition that came out in May. (If you observe the photo on the left, you will see that the imitation leather is on the left, while the hardcover is on the right.) Needless to say, this is a disappointment. Why even produce a cover like this one when you already have the hardcover edition? That simply doesn't make much sense to me. I would have much preferred that they simply used bonded leather, like they utilized in their NRSV thinline Bibles. Actually, I really liked the feel of the NRSV Compact Thinline, which came out in 2009.
Ultimately, if you are desiring an edition of the NABRE, the hardcover one is the way to go. It is too bad really, since I believe that HarperOne has created a very attractive page layout with their NABRE. Its a shame that they never completed the package by producing it in a good leather, or even imitation leather, cover. Again, stick with the hardcover edition.