Question: "I would like some advice on which power monitoring solution will be best for my need. I have a granny flat with a sub board. From this sub-board I have one circuit that has my pool pump. What I would like to do is to monitor the whole sub board, then subtract the pool pump circuit."
Answer: To monitor the total power use going to the granny flat sub board I would recommend installing an electricity sub-meter.
Then, to monitor your pool pump, you could use another sub-meter on the same sub board (if space allows). An alternative option would be to use a plug-in power meter such as this Smart Plug With Energy Monitor, which can be set to run at specific times using the timer function (note: dry area installation only).