I got a new bag last week, the Big Pod from MEC. I had been using the Sling Pod for many years, maybe 10 years now and making the switch has been pretty easy. Both bags work the same way where you just slide it upwards to get to the zipper pockets. The inside pockets are virtually the same as those in it's little brother, just a little bigger.
What's nice about this bag is that now I can put my umbrella in without stretching it, and I can still fit a bunch of other things in it. For example I can roll up a windbreaker and fit it inside, and still be able to reach other things in the bag, whereas before once the windbreaker was in there, there was no room to do anything else.
Other than size, the major difference is that the side pocket for a water bottle has been removed. Instead there's a zipper there and when unzipped, a pocket folds out, but this pocket is not deep enough to really put a bottle in there. I have no idea why they changed the design, because with a larger bag you would think they would make a pocket for a larger bottle of water at the very least.
Minor differences are the material does not seem as thick or sturdy, but I have a feeling the Sling Pod is the same way now.. I was spoiled with one of the original sturdier Sling Pods.
That's about it, not much else to say.