There is no set answer, because everyone's environment is different. You'll just need to test it for yourself and see.
First, do speed tests with and without the secondary mesh node. Run a dozen in each configuration to get a usable sample size. Use different speed test sites too.
Then do a continuous ping test to your Default Gateway (your router's LAN address, for example 192.168.1.1 is common, but just check) with and without the secondary mesh node. Run that test for an hour each or more during busy network times, like in the evenings. Compare the results.
Then see which you prefer.
The placement of your mesh nodes, test computer, how busy your WiFi is in general, and layout of your home will determine test results. So there is no set answer.
I will say that, with wireless backhaul, you should just use the least number of nodes you need for full coverage. Four seems excessive. Most homes need only two mesh units to cover everything, three for bigger or unusually shaped houses.