For one unit, we recommend you install it somewhere central. Most people usually use a location close to the electrical breaker box as it’s more convenient and out of the way. However, as long as it’s somewhat centralized you’ll be fine
For multiple units, we always recommend installing them as far away from each other as possible. Ideally, at opposite ends of the home. This will allow you to maximize the effect of the devices.
Placing the devices close to the circuit breaker is ok but not required. Most people use that location simply because it's more discreet and convenient.