Don't feel stupid. The same confusion happened to a lot of us when we first switched to refractometers. If you don't have an unbroken hydrometer handy, you assume your calibrated new toy gives a good measurement of FG, like it did SG.
I have wasted $ in the past getting more yeast when my primary airlock fails to bubble, only to pop the bucket lid and see active krausen. Buckets often have slow leaks in the lid, especially if you've pried the lid off in the past.
I've brewed with both a banjo-style burner and a jet-style burner. I think the jet is louder, but the advantage is that it is more efficient. At least it throws off less heat outside your kettle. To illustrate this point, a buddy and I used to brew with keggles and a banjo-style burner...