Got one for a Labrador (working female i.e. small for lab). Looks like a really good thought out back pack, with padding over the buckles and lots of adjustments in the straps. Two zipped compartments with room in each for a 4 pint plastic milk bottle. Each compartment has a black mesh splitting it in half, presumably to stop things moving around too much. One compartment has a clip for keys or poo bags or whatever. We got the red one and it has several handy reflective stripes. Being picky it could have done with the strips continuing round the pannels at the back (as they do with the front) so reflective from directly behind (I suppose they have to be small to only see this bi)..
The whole thing though is let down by those buckles. There nice and big so pressure is spread on the dogs body and seem secure when not on the dog but when you clip them on the dog there engagement doesn't last and they keep coming undone making the whole thing a bit redundant. I got fed up with them after a few months and tried to bend them to get more purchase and managed to snap one. I may try to replace the buckles with (large) ruck sack replacements and see if that's any better.
May be we just had a duff one but if they're all like it its not going to be very good. If you get one keep your receipt in case its no good. (We didn't purchase our's from Amazon).