Hi mou mou,
I've had a couple of pairs, both in box, and one pair stretched a bit more than the other for some reason, but I wouldn't say that they stretch a great deal. They're cut fairly wide, which for me wasn't ideal, but I found that the "H" structure prevented back slippage.
The soles are leather, and yes, they're quite thin (and can be slippery too until you scuff them up a bit.) When I got the second pair, I had my shoe person add a Vibram sole to them, which prolongs the wear and makes them more comfortable too.
They are comfortable, but I did get a blister on one toe until they were broken in (maybe because they were a bit too wide?). They're great for casual wear, but I wouldn't suggest walking long distances in them over hard paved streets, etc. due to the relatively thin soles and the fact that they offer little to no support for the feet.
I've found that I now prefer the Oasis to the Oran, as it has about a 1-1/2" heel, which for me, at least, is more comfortable.
But, the Orans are great too. I literally wore mine to death!