Well, all things being equal, if I had to choose between 600 cranking amps and 800, I'd probably opt for the 800.
I think the weight is irrelevant, at least if we're talking about a difference of 1.4 pounds. These bikes are hippos, so 1.4 pounds isn't going to make a difference. Dimensions are more important than weight, I think, since storage space on a motorcycle is always limited. If i had limited space, and the 600 amp battery was smaller, then I'd feel fine with using it instead of the 800.
I had one of these portable battery jumpers for a while. It was a Pilot Instaboost. I believe I used it four times over as many years, and then it failed. Even when it worked, I had to send it back to the company for warranty work when a diode failed.
These jumper packs are something I'd want to carry only under certain circumstances, like if I was traveling alone through a very remote area where it was unlikely that somebody would happen by if I had a battery issue. Unless you're pretty detail oriented about maintaining things, a rechargeable battery booster is the kind of thing you throw into a trunk (or pannier) and there is sits, for maybe years, without you ever checking the battery level. Then, they day you actually need it, it's as dead as the battery on the bike.
I carry a set of mini jumper cables in my crash bar bag. I had to use them last summer in Virginia, where I jump started my bike off a kindly stranger's F250. Jumper cables pack small, there's almost always someone around that can provide a jump (unless you're in the aforementioned remote area), and they never go dead sitting in a pannier.