I purchased my K4 3600 system a couple months back. They shipped it to be in Qatar, where I live and work. Super fast shipping. I trained with it for 6 weeks with up to 80 lbs in the back. Super strong and well built system. Improvement over my Kuiu icon pro. I flew to CO for my week long elk hunt, and used this pack every day in the mountains. Absolutely loved it! 2- miles a day hiking up and down hill at 10-11k elevation. Unfortunately, I didn't get an animal this trip, but I still used this pack hard every day with 30-40 lbs at times. I'm 6-1, 215 lb with a long torso. I used the large belt, with 25" frame with rifle straps, and it worked perfectly. no hot spots, no sore back. My bladder leaked one day, but the water resistant bladder pocket did its job and kept the rest of the pack and me dry. I used the pack almost every day to sit on and glass, and it held up great. Only thing I think could be improved are to add another zipper on the hood/lid large pocket. I kept finding the zipper on the bottom somehow, and it would be nice to have one zipper on the opposite end just in case you find yourself with your bag upside down or flipped over. Very happy customer. I also wish that Exo could release a toddler carrying system for the off season/training/vacation. I (and others judging from the comments on YouTube videos) would use this all the time! The baby and toddler carrying options out there are vastly inferior to this shoulder and belt system.