I'll take a stab...but I'm not going over to the Ibex site to look at that bike. I'm too lazy, and you were too lazy to post a pic...LOL...just jabbing you. From your description I take it that the Atlas mounts the shock on the front downtube. So for equality let's compare it to a Bullit vs. Heckler setup. In reality the important issue is where all the "dots" of the suspension points are on a piece of paper that determines how the suspension rate or characteristics function. For this very general comparison, the Bullit's suspension rate is fairly linear with a slight falling rate...also depending on where you mount the shock in the shuttle...it has two positions. The Heckler has a very strong falling rate and is very sensitive to the type of shock it uses because of that. Most of these (I'll refer to them as Bullit clones) bikes with the front end of the shock mounted on the downtube are usually more linear while a design like the Heckler is more falling. This isn't always bad, as you can tell the Heckler is very popular and performs well.
Now, much of this generalization goes out the window as the pivot points change dramatically or you throw a linkage in there. There's no really straight answer here as to what's best or not. And if you're not familiar with falling, linear, or rising rate as it applies to the rear suspension, then that's another element altogether.
