Why are aquarium heater reviews so mixed?

As one r/Aquariums thread puts it, you shouldn't over-weight one or two one-star reviews when the overall picture is positive, because every brand has failure stories. Heaters are consumable safety components, so even well-reviewed models accumulate dramatic failure reports over time. The reviewers we read suggest watching for patterns (consistent inaccuracy, shocks, or shattering) rather than isolated complaints.