most efficient way to trigger device

[HwpFEr2vbuAhbpbjqQ27eorCWn]

simple scenario: thermostat SHELLY H&T PLUS GEN3 to turn ON (upon temperature drop) SHELLY SMART PLUG PLUS S GEN2 using SHELLY APP

question: what is the most efficient way to achieve this? (considering the batteries of H&T - as I read somewhere that most efficient is to setup RPC url, and worst is to have it CLOUDed as it will half the life of the batteries). the simple scenario can be achieved with any of these triggers:

1. ACTIONS of H&T thermostat
2. ACTIONS of Smart Plug
3. SCENES
4. THERMOSTATS

the only trigger where I can input RPC URL is ACTIONS so does it mean:

1. ACTIONS is the best way? if so, which one: ACTIONS of H&T thermostat to enable Smart Plug? or ACTIONS of Smart Plug to check H&T status and turn on itself?
2. or both ACTIONS from above are equal?
3. SCENES and THERMOSTATS do not use RPC so they are not efficient? or they do use RPC, but internally? both? only one of them? which one?
4. or all 4 above triggers are equal in terms of efficiency and reliability? eg. it does not matter which trigger is used as they are all the same thing, only called different to confuse the user?

thank you in advance for a quick and detailed answer!