Reporting back for a review, for anyone who might care to know, and to ask for other recommendations.
I bought a pair of Altra the One 2.5. I have to say that I am generally disappointed with them. I've run about 50 miles in them, and I think that's plenty enough to draw some conclusions:
1. Altra and many reviewers says they are built for speed, but I found that the cushion was so spongy, that this factor alone will prevent me from using them for anything as fast as mere tempo pace. I like to run fartlek, at many paces, sometimes finishing my runs with strides at near-top speed. These shoes can't handle the pace, so I guess I will have to use them for my recovery days only.
2. These shoes are fairly flexible, but not nearly as flexible as you would think by looking at them. In addition, I found that the flexibility didn't do too much for me, because the sponginess of the cushioning seemed to really such the energy out of my step.
3. The upper seems to bunch up in the forefront. Not a lot, but enough to be annoying.
4. I do really enjoy the fit of the upper in the heel and the shape of the last.
5. The toe box was by far the best feature of the shoe, very good. I wouldn't change it.
6. These shoes are zero drop, but I believe they have a bump in the middle, probably for arch support. I have low arches, and the bump makes the back of the shoe feel like it was sloping backwards. Made for a strange feel, also not conducive to speed, since it seemed to mess up my foot strike fairly badly (I strike midfoot to forefoot).
TL;DR: Altra probably needs another shoe in their lineup. I would go right out and buy a shoe that was firmer, with a slightly upgraded upper, if they provided one.
Any more suggestions out there?