Thought it was time to report back on this thread. I finished up by wearing my Ecco Off-Road hiking sandals for the whole of the May/June Camino del Norte (840km), and September
Camino Frances, including in the wet and through muddy tracks, and on hard roads. For me they worked well. They have a tough purpose built sole which shows not the slightest sign of wear. I tended to wade through mud and water without concern. If it was very cold I wore Sealskinz waterproof socks. Otherwise I did not wear socks. My friend who was walking the
Camino Frances for the first time, on my suggestion, also wore Ecco Off-Road hiking sandals, but with socks. She found them perfectly comfortable and I can't recall her getting any blisters. I did not. Neither of us had problems with getting stones or pebbles inside the sandals, the pebbles just shake out, although it was a little more difficult with socks.
I have bad knees from old skiing accidents, and broke my ankle several years ago, but my trekking poles give me all the extra stability I need.