I bought it for 31€.
The truth is that it's worth 10€ less.
I thought for some reason it would have its own battery to charge wirelessly, but it was my mistake.
The reason I bought it is because I wanted to have 4 joy-cons for multiplayer and 2 controllers for when I play with my partner.
It's difficult for me to play while the cable is connected to the device because it's near the TV and there is a distance of 3.5 meters from the couch, as it is a 55-inch TV.
The cable is about one and a half meters long, if I'm not mistaken.
I connected it to my laptop, which was next to me because of work, and it worked perfectly.
In summary, if you want to have 4 joy-cons and you play a lot, it's convenient.
If you want to have 4 joy-cons and 2 controllers, but that's it, it's better to buy a cheaper licensed product.
If you don't want to have 4 joy-cons, then it's better to get the pro controller for the switch, which is the best compared to all the controllers for the switch.
The first solution worked for me, but it's not for everyone.

I do not understand the reason for the existence of this grip, especially at this price, it charges the joy-cons without needing to be connected to the console, it does not have any other function or use

It offers the ability to charge the Joy-Con either while playing or when the console is closed and they are connected to the Grip. Expensive compared to what they offer.