I was interested in the Mission as well when I was shopping for trailers a couple years ago. I was set on aluminum and started out looking at Featherlite as their quality is unmatched, but their prices were out of my budget.
Mission caught my eye since they had a lifetime warranty and looked to be high quality. I found a dealer that had one on the lot and went to see it in person. I walked up to the trailer and the first thing I saw when looking down the side was two broken off heads on trim screws and one of the rivetless seams on the outer aluminum skin had separated about 8" starting at the top of the joint.
That was enough for me! I figure if they let visible details like that go out the door, what is the quality control like on the wiring, welds, and other things that are hidden like?
The one I looked at was made in Maine. If they are now made in Montana, maybe the quality control is better, but I would definitely not buy one without seeing it in person.