First he doubled a VGA output: It is possible to connect two monitors or projectors that then both show the same image. This works with a variety of resolutions - the manufacturer's maximum value to 2048 x 1536 pixels. I have not tested this, but I am encountered at lower values to settings that do not support the splitter. With the current standard resolutions it has but always worked.
The connected splitter identifies itself to the PC as a monitor, even if its two terminals are not connected. This can be useful, the off the VGA output without recognized monitor or switch especially in those notebooks.
Whether the device is actually capable of as an amplifier for the analog VGA signal to improve image quality with long cable lengths, I can not judge. The manufacturer specifies up to 55 meter long cables are operable with the splitter. My experience: Even when connecting projectors in large halls there was always einstabiles image.
The power supply via the USB port is a clever idea to save the umpteenth power adapter. Especially since the port is durcgeschleift and thus (with reduced current capacity) is still available. Processing is true: All VGA plugs and sockets have locking screws, the mechanical precision is sufficient in order to use "non-violent".
Conclusion: does what it promises. Works reliably. And all for little money. So five stars are earned honestly.