I'm certainly not an expert, but I doubt that anyone is, since everyone's feet are different, and people seem to have wildly different experiences with the same shoes.

I have used the Altras, though, the Lone Peak 3.5, and like them a lot. They're probably the most comfortable shoes I've ever had. It took me quite a while to get used the zero drop, probably four or five months of daily walks. If you're used to Birkenstocks, though, you may not have any problem. Years of wearing shoes with an elevated heel cause your calf muscles to shorten, and it takes a while for them to stretch back to "normal." So, calf tightness and soreness was what I experienced, especially after lots of uphill.

I have no experience with Altra's waterproof/breathable shoes. I have used the Keen Targhees, which are pretty good, though certainly not zero drop. Maybe worth considering if you decide against the zero-drop shoes. And not terribly expensive, as boots go.
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The Altras seem to run slightly small, and aren't very consistent between models (I tried on several, looking to replace my first pair of Lone Peaks.) So, best if you can try them on, or at least make sure they're returnable.