The mouse mat is not waterproof. It is made of plastic and has a rubber coating on the underside, which makes it non-slip but does not make it waterproof.
If you compare the two, you will see that this one:
L:400 mm
W:900 mm
H:3 mm
has. And the one you have attached in the link has:
L:435.4 mm
W:900 mm
H:138.3 mm
The Logitech G840 is like the G640, only bigger. You're more likely to find comparisons if you search for them.
The Logitech pad is a lot faster than the QCK, especially when new, in terms of both static and dynamic friction. The QCK feels like a "mudpad" compared to a new G640/G840, good for games like CSGO/Valorant but tracking heavy games like Apex or Overwatch are a bit harder. However, since the Logitech has a coating, the pad becomes a lot slower and inconsistent after a while, especially after washing. Generally advise against coated pads unless you want to get a new one every few months or don't play shooters so you don't care about the inconsistent glide.