The IS huaraches are very flexible, only 4mm, and I have decent ground feel, but not the best ground feel, which will be difficult with any layers between your skin and the earth.
I wonder why the Luna folks would say that theirs would be too floppy; the ISs are just fine.
The IS have more ground feel but are a bit floppier. I now run in naked lunas sometimes and like them. I haven't tried running in my equus yet, well other than sprinting after my dog.