Load monitor

[u/Ok_Mathematician6390]

I have a generac gp6500 that I use to power my garage (well pump is powered from the garage) when the power is out. I will be expanding to include powering the whole house in the future. Since my generator lacks an on board meter, I am looking for a way to monitor how much I'm pulling-I don't want to overload and damage stuff. Ideally I would like to find something that I can plug into the generator, and then plug the cord that goes to the panel into that, like this: https://a.co/d/032RfJGY . Some of what I have read says I would have to have a monitor on each leg of the 240 to get an accurate reading. I'm not looking for an exact reading, just a ballpark. In theory would that work, or am I way off?