Tried the Zems for a while. The stiffer soles were good for protecting the feet around the tent at night.
But for crossing streams, especially freezing cold, raging ones? Never in a million years. No traction, and they would get sucked off in real muck. Straps, front and back, are a must. Ditto for the 5-toed thingies.
There are a lot of good neoprene water shoes with heavier treaded soles, but the weights are prohibitive for BPL.
I think the answer lies in a sandal with the lightest possible EVA sole with a good tread on the bottom, and the lightest possible harness that is strong and well designed enough to keep them locked on, and does not go between the toes, so you can wear the lightest possible neoprene sock to keep the feet from going totally numb in cold water conditions. Have found that losing feeling in the feet during crossings is not just unpleasant, but extremely dangerous with boulders underneath.
Would have made something by now, but don't know how to attach loops or other harness keepers to the sole. Can't stick them in from the bottom, because don't want anything on the bottom but the tread. And EVA is on the fragile side, so it is hard to figure a good top attachment.
Bought the lightest EVA-soled thing on the shelves at W-Mart. It has a canvas top that would just get wet and heavy, so it will be cut away except where strap attachments are needed. But will do it only if the weight will be well under that of the TEVA Mushers. If not, well – as some of you know, the BPL threads on this topic are legion, and attempts to invent the wheel occur several times a year. Eventually, the wheel will come.