Length basically. The MS doesn't seem to weigh a whole lot more than either of those tents and it has two doors where the Kelty only has one. I'm 6'4" so I had put a minimum length of 90" on any tent I would consider. If I were shorter there were loads more options. I was strongly considering the REI Quarter Dome T2 Plus and was going to wait until I could save up the $300 but then I found the MS and decided that was the tent for me. I can comfortably fit me, my two kids, and our gear in this tent. I think I can also fit my dog. Anything substantially lighter that still met my criteria was a whole lot more expensive. I really liked the specs on the Big Agnes Fly Creek UL3 but $450 was too steep.