Not anymore! I just got a message that it's back IN stock! I would order it if I were you... I'd do it too, but the shipping is too expensive for me now. I just hope that it's stil available in the beginning of september
The strap is adjustable. And how many binders do you want to put in the bag? Because it depends on the width of the binder. It is this kind [link] or this [link] If the binders aren't very wide like in the last picture then the bag could fit about 5 binders maximum: in the normal place and 1 in the laptop holder. But I suggest you not to put 5 binders in the bag. Because each binder does weigh something and the bag wouldn't hold it. So put maximum 3 of those binders.
On the other side if the binders are very wide like the first picture then the bag could fit about 2 binders maximum.
I hope this information is helpful. I've ordered this bag around New Year and I've tried with my own binders how many it could fit.