Complex sentence: While the Six's thermometer has many advantages over other types of minimum-maximum thermometers such as electronic and bi-metal variants, it contains mercury, which is environmentally harmful if broken or disposed of improperly and therefore banned for most uses in some parts of the world.
Split into simpler sentences: While the Six's thermometer has many advantages over other types of min/max thermometers such as electronic and bi-metal variants it however contains mercury which is environmentally harmful if broken or disposed of improperly. Because of the environmental issues connected with mercury it is banned for most uses in some parts of the world.