Why does any of this matter?
Because you are going to keep something under your lip every day for the next ten years, and the ingredient panel is the whole decision. Everything else about the habit is identical either way.
That is the good news. Nothing about your day has to change. One line on the back of the tin does.
Rule #1: Turn the tin over before you buy it. The front is branding. The back tells you whether you are buying a nicotine strength or a mineral, and those are not the same purchase.
Rule #2: Check the actual active. Nano-hydroxyapatite is the mineral your enamel is already made from, close to 97% of it. "Whitening" printed on a lid is not an ingredient.
Rule #3: Watch for strength tiers. Anything sold in escalating milligram steps is telling you what it expects to happen next. One formula, one amount, and a printed daily ceiling is a different kind of product.
Rule #4: Check the guarantee and buying options. Bundles, an optional subscription you can cancel anytime, and a 30-day money-back guarantee mean you can run a real test.
Rule #5: Buy from the official shop. Steer clear of random resellers, cheap knockoffs, and tins you cannot verify.