Very simple and practical works in 10 minutes

Do not put it too close to the box or router, do not hesitate to repeat the setting as it is sensitive to where you use it.
Works without problems on Mac OS X.
It is directly plugged into a socket, it waits until the green LED is on, then we see appear a WIFI network that ends with _EXT
It should connect to it.
Once you open a Firefox or Safari browser, the setup starts up and guides you through the setup, it's really simple: choice WIFI network to expand, for example FREEMAISON and it creates another network to which the devices FREEMAISON_EXT can connect with the same password everywhere.

In my case, it serves primarily to catch the best network to a place where I had no bar to an IP camera WIFI as impossible to pass an ethernet cable at this location.
I tried behind a large bearing wall and it works too.
If you have a small network in one place, it will stabilize the connection but not increase throughput phenomenally either.
The ideal is to install it halfway between your box and the device.
The advantage of this model is that it offers in addition an Ethernet port on the side to connect directly to a PC or camera without wifi but just with their cable.