Cary's comment is right on - sagging is a feature of silnylon. The more of it, the more stretch. The SMD utilizes a lot of material.
Rafi, regarding that review, if that was their experience then it is what it is, as the saying goes. However, from reading that review I notice a few things. They dinged the tent for not having a rain fly and being a single walled tent... well all I can say to that is duh! I get the feeling this person didn't research of understand the differences between single wall and double wall shelters and their expectations were not realistic. I don't find the tent difficult to setup, nor would I have a problem setting it up in the rain (why would this make setting up any tent more difficult??).
Personally, I have not used the LH Duo that much. It doesn't vent quite as well as the SMD in my experience, which can be a little breezy. It is a roomy tent, but the SMD is king when it comes to room for two... it also has a big footprint, which can sometimes be a challenge to plop down in the woods.
Judy is putting peak vents into the SoLong 6 (nice tent, by the way), so I have to wonder if the Duo will (or has been) updated to include them too? I think Judy is on vacation (or possibly traveling for business) but I'll see if I can get an answer on that, I'm curious now.
edit: Talked to Judy briefly, the current design of the Duo does not have peak vents. It sounds like she has plans to implement the same sort of vents that the SoLong has, but didn't give me specifics on when that would happen. Judy is generally very easy to get in touch with. If you have any questions I'm sure she would happily answer them.