Nice Smoke Adam!
So here's the scoop on the Mini, and the diffusers... High temp smokes, on the upper rack the steamer insert is fine, or not even needed. Yeah I said that, not needed. Lower temp smokes or when you want to smoke a couple different things, you need a diffuser to block the heat. Not an issue if you only use the top grate, but once you start using the lower one, you need that buffer. Also when smoking at lower temps and the outside temp is low the extra mass helps regulate heat better. With a diffuser that has mass to it and covers the bulk of the firebox I can get the upper rack, and the rack at the insert lip level within 10-15 degrees if each other, without a diffuser the lower rack is at least 30+ degrees higher.