There's a thin line between a flourishing product category and an oversaturated one. The smart thermostat racket is fast approaching critical mass, and energy providers across the UK have begun offering hi-tech heating controls to their customers through in-house products, rebrands and various partnerships. Today, it's First Utility's turn. The energy merchant will now give anyone signing up to its three-year, fixed-rate tariff a free Cosy smart thermostat plus installation. Born from a successful Kickstarter campaign, Cosy has a familiar feature set, with programmable schedules and remote heating and hot water control via smartphone apps. Obviously the cost of the tariff should be your primary concern, but if it makes sense, a free Cosy might be handy if you haven't already got five smart thermostats at home.