Water Heater - Do I Need 1 or 2 Hi-Limit Reset Switches?

My Bradford White water heater has been tripping every morning so I'm on my way to replacing both upper and lower thermostats. The upper thermostat is an Apcom WH10-A double-throw with a hi-limit reset, and I will replace it with the exact same model.
The lower thermostat is an Apcom WH-9 which is a single-throw without a hi-limit reset. However, Apcom also has a similar model WH9-6 which appears to be the same or compatible replacement thermostat but with a hi-limit reset button.
The question is: would the lower thermostat with the red reset button be a better choice than the one without the button, given the fact that the upper thermostat already has an existing red reset button? Cost is not an issue since we're talking just 5 bucks price difference. What's the point in having 2 hi-limit reset buttons, one for each thermostat? Is this a good idea?
Any advice would be appreciated. Thanks.
P.S. It was 26 degrees F in DC this morning - bitterly cold, in my experience, and this could be causing my water heater to go bad.
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wrote:

No real need for an overheat button on the bottom one. The top thermostat is the master thermostat and the overheat button on it cuts power to both thermostats. Since heat rises the top thermostat would cut power long before the bottom of the tank would get hot enough to trip the safety. The "bottom" thermostat with the safety is probably used for small single element water heaters.
26 degrees isn't bitterly cold. A large amount of the country sees these temps for months of the year and they all have hot water. Even at that the thermostats are at water temperature since they are held ot the side of the tank and covered in insulation.
Steve B.
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