Using the same concepts from the Jumbo KISS, it was pretty much a no brainer to apply them to the Fatboy, the result being this GTG (Good To Go) variant. I would have just stuck with the KISS name variant, but I suppose it helps makes a distinction between the Jumbo and Fatboy. Anyway, the main idea appears to be get costs down while still keeping the core functionality of the bag intact, which I think it does well. Generally small details are taken off such extra webbing and dividers to achieve this while keeping the same overall size and layout. These changes along with using 800D as the core material achieved approximately a 25% weight reduction. The 800D is slightly more flexible compared to the usual 1000D Maxpedition uses, however is still plenty strong to achieve long term durability.
For some of the other changes, the shoulder strap is now 1.5" rather than 2" and the HK snap is a simple plastic D-ring. Ladies will probably like the more slim strap, but those who weighted down their Fatboy may miss the wider 2" strap for long wear comfort; Don't worry the shoulder pad is still included. The phone pouch and extra webbing have been dropped for simple webbing zones with loop to allow patches or Maxpedition sheath pouch attachment. Due to requests in the past a drag handle has been actually added. Rather than a belt snap, the back uses a velcro flap as seen on the Jumbo series. The result will likely be more comfortable for most as the velcro flap lays more flat against one's body. The same back mesh padding is used which is comfortable, however definitely the durability weak point on the bag having the least abrasion resistance and gets thrashed by hook velcro. As a more substantial change, the secondary compartments are totally different. The GTG now has a water bottle pocket and a GP pocket where the original fatboy had the GP pouch on the other side and a flashlight / sheath pocket. It will depend on the user, however I think most will welcome the addition of the water bottle pocket. Personally I'd rather have the water pocket on the other side so easier to access when worn on the right-hand side, the balance I suppose is the GP pouch would be a pain to access (requiring bag shifting for most) if that was done. On that note, to swap the layout there is the option one could get the S-type (lefty) version and just wear it on the right, just keeping consideration the CCW zipper will open the opposite direction. Sadly there is no grommet on the bottom of the water bottle pocket, or anywhere on the bag for that matter, but not a deal breaker.
Another big change is the removal of the draw-string closure on the main compartment. Some will miss it as it help keep smaller items secure, while some will be happy to see it gone to have more snag free access. The CCW zippered compartment appears overall the same keeping a good size loop field in there; Great for compact or smaller pistols. On the frontal pocket the core is the same with the interior having divided elastic webbing rather than a sleeve divider.
That about sums it up on differences. It is nice that rather than being just a dumbed down version, the GTG changes offer some options that some people may prefer. Overall a great variant to get the price down while keeping the core functionality and size class of the bag intact.