I actually ordered this from Love Boat thinking the same thing. It looks like it can hold a lot, make it flat, and keep spillage under control.
They recommended an x-large for me, I ordered a large.
It was way, way, way too small. Even if I had ordered a XL, it still wouldn't have fit. I called them and they told me that that model is usually for smaller framed FTMs. I was like really? It doesn't look like it from the picture, but oh well.
Here is what I would do, because every body is different. Get their e-mail and tell them you need help sizing for that particular binder.
They have EXCELLENT customer care and would be more than happy to give you their opinion of what size or model they recommend.
They may ask for your measurements, don't be shy. And they will probably give you a few "best" options to help you chose.
I mean, afterall, it their product. They'll know best.
They helped me a lot, and I think its your best bet.