I own a Bullet ultra lite, not a Bullet Premier. We as a family have been in it about 50 camping days this year so far. Haven't had a warranty issue yet. I've done a lot of upgrades to it to get it where I want it (nicer faucets and diverter, backsplash, hitch, large wheels and tires).
But in terms of quality, many of the brands being produced by the same manufacturer come off the same assembly line. I think the Premier model is built like the Bullet ultra lite but they include a fiberglass front cap and higher end finishes on the interior. This adds to the Premier's weight and price. Look at dry weights for the same floor plans on Keystone's website and you'll see the Premiers are overall heavier. The skeletons are relatively the same; it's the skin that changes from model to model.