I can't speak to the K4 but I can speak to the KUIU frame/bag setup. The KUIU frame feels great! That is until its loaded down with enough weight to warrant a pack frame. I have two issues with the KUIU frame.Can someone who loved the KUIU Pro Frame and bags tell me why I need the K4? Thanks
The first issue is the carbon frame doesn't allow any torsional freedom of movement. It feels like having a sheet of plywood strapped to your back. Not super fun when you've got a few miles of blowdowns you need to climb through.
The second issue I have with the KUIU frame is the lumbar pad is waaay too firm. On super heavy loads it just digs into the base of your spine. After a mile worth of hiking with 90 lbs made my legs start to tingle and I was sore for a few days afterwards. It's entirely possible they've re-designed it since then but that was my experience.
I absolutely love the K3 over the KUIU system but I'm curious what advantages the K4 has over the K3