It is a very beautiful bag. Quite waterproof. I have helped it with many layers of Duro Stick waterproofing. I carry it 365 days a year with a backpack, even if I get out of the car to go to the kiosk or a restaurant. I decided to get a "winter" bag because its sides are not mesh and they close with a waterproof zipper. It also has a compartment for an umbrella and one for a water bottle. Another reason I bought it is for skiing in the snow and I really feel that my belongings are safe.
The liters indicated are cumulative. It has many pockets, small and large, which obviously take up space from the adjacent ones and thus it appears - it becomes much smaller in capacity by necessity. It has a strap to attach to the handles of the suitcase and a "hidden" pocket on the back. I have a 17-inch laptop which only fits in the main large pocket. The compartment intended for the laptop has velvet lining and a velcro strap on top, and it fits up to 16 inches.
To fully utilize its capacity, it requires many trials of where to put what, but in the end, you will settle. It is comfortable and has a small pocket to put the owner's card.
Personally, I am fully satisfied. I have the nickname Sport Billy and not without reason.
As an indication, the bag permanently contains: an umbrella, masks, a 20000 PowerBank, charging cables of all sizes, 3 sets of cutlery, 2 disposable toothbrushes, tissues, antiseptic wipes, a flashlight, a multitool, various basic medicines, betadine, Hansaplast spray, eye drops, etc., all distributed in the various compartments. The large space is empty and available depending on the day and what I have to do.
I hope I helped you with my comment.

Purchased for everyday use and overall I am very satisfied.

Durable construction, with many pockets for items, waterproof (tested in a recent downpour where books and papers did not get wet) and quite compact (not bulky).

One of the negatives is that the main compartment can fit 2-3 books, 1 tablet, and 1 laptop at best (although you can tell how "tight" it is), in the external pockets for umbrella and bottle, the bottle should be slightly slim to fit comfortably, otherwise it takes up space from the inside and the umbrella should be small (I use this one: [insert link]).

In summary, the backpack is of good quality and comfortable but not meant for carrying a lot of things.
To get an idea, watch a mini presentation of the manufacturer on YouTube: [insert link]

ATTENTION!!! The backpack does not have a USB port as mistakenly stated in the description.

Update 31/08/2022: The backpack was tested in another downpour and once again it came out unscathed as nothing inside got wet!

Update 21/09/2022: After a 20-minute walk with an umbrella in today's rain, the book inside got wet... Ultimately, it's not suitable for heavy rain. Now it's a three-star rating