I bought these for my afghani tour. I wanted shoes that could slip on in an instant for emergencies and that would also be comfortable in the heat -this shoe does both very well.

The bottom half of the shoe (including the main part of the heel cup) is made of breathable nylon supported well by the strips of leather. The attached sole's tread pattern helps ensure good footing over the dirt and 1.5" gravel walkways that are everywhere.
The top of the shoe is comprised of a neoprene material which includes the "tongue". To better visualize the manufacture, imagine a water sock upper built onto a running shoe.

As for slipping on, the concept is genius. On normal shoes, the heel cup is generally stiff up to the ankle requiring a finger between the shoe and foot and/or some side-to-side foot maneuvering to get your heel down; I've always disliked loafers or slip on shoes for this reason. Not so with these shoes, since the top half of the heel cup and tongue is neoprene, it expands just enough to slip the foot in.

The laces are a thin bungee material to bind the front together and is adjustable with a spring-loaded clip allowing you the freedom to customize the tightness to your liking.

Fitment:
I wore these out-of-the-box when they arrived in the mail and was initially concerned about the overall compression I felt around my foot, but within 8-hours these broke in nicely such that I had to tighten the bungee laces a bit. I usually prefer a wide 8.5 EEE shoe if available (provided it doesn't shrink after washing) but normally I buy size 9 shoe with a good arch support.

I  feel these shoes are true to size and not too narrow. The arch support is good and they don't feel like wearing flats. When I kick the ground with my heel (at an angle) to set the heel back into the cup, I feel approx 1/2" of space in front of my toes.

When walking the shoes hold well and my heels do not feel like they slip out more than a regular shoe. I wouldn't recommend thick socks with these however, you may feel like there is too much compression. The thinner underarmour type socks compliment these shoes really well. I did notice the shoes slipping about when pushing and heavy trailers around, but this isn't something I do regularly and it isn't a big concern -i suspect I could adjust the laces more if need be.

Overall, I am very satisfied with the shoe. The sole stiffness is a nice blend with enough flexibility to bend but holds well in large gravel. The slip on design is great for my needs and I imagine would be equally great for beaches and hiking without slipping too much. The lower part of the shoe is ventilated enough I can feel a breeze passing over the foot providing a nice cool sensation. I love this shoe and am considering buying another pair.