Quite a beast, thin and therefore not heavy but wide and therefore durable, so it doesn't strain my lawnmower.

The blades it has are extremely sharp, so much so that you're afraid to grab it to install it. It's suitable for simple grass and even slightly woody weeds, something that regular trimmer line, the star blade, or the disc (which many lawnmowers have) can't handle, as each one is made for a specific use.

--- The trimmer line cuts by "whipping" the grass, which is why it's only good for thin grass.
--- Other blades that aren't THAT sharp cut by "battering" the weeds, making it harder for both the user and the machine.
--- This one just slices them simply and nicely, because its sides are serrated like razors.

All this also relates to its price... about 4.5 euros! It pays for itself with the first mowing and very easily because you don't have to constantly change the trimmer line, and it's economical because it hardly wears out at all. It will last you for many mowings before needing replacement, maybe even years depending on what you mow. I was mowing the grass and would stop out of habit to check if it needed anything, and I was happy to see the blade keep going strong! Also, it can be mounted either way because all four sides are exactly the same, so if you see one side starting to wear, just flip it around.

Don't use it in areas with stones and not too close to the ground so it doesn't hit and get damaged.
You'll see the convenience it offers if you want to mow a large area with very tall weeds.
I don't even know if it can be sharpened because the edges are serrated, but for 5 euros, if you think it's worn out, just get another one. Buying one of these a year isn't expensive; the trimmer line over a year will probably cost you much more.

Excellent disc. It cut thin grass, grass with a thickness of 2cm, grass with woody stems, and overall weeds, as well as thin branches. Because it is thin (1.6mm), it allowed the trimmer to work at lower speeds without any strain, resulting in fuel savings. Where I needed about 4 fuel refills, I only needed 1.5. I used it, as I mentioned before, on a variety of grasses and saved the cost of the trimmer line. I would say that the trimmer line I saved almost covered the cost of the disc. On the other hand, because it is thin, it requires caution with stones, iron, etc. so as not to bend (I hit a 5cm thick iron pipe and it scratched it, but it cut it without bending... I hit a wall, though, and it bent slightly at the edge...). It is important that it is 355mm, because it "shaves" a larger surface compared to most 255 or 300mm discs. Finally, with its performance, I saved a lot of time. It may seem like an exaggeration, but the reality is that a job that took ~8 hours, I finished in ~3 hours. Compared to other discs I have (3-blade with pointed ends, 3-blade with "square-straight" ends, round with 40 teeth, round with 80 teeth, and a destroyer (double-blade with bent ends downwards), it is much better for a wide variety of grasses with a thickness of up to ~3cm. I will now use it for the majority of the field and use trimmer line for the edges and near "dangerous" materials. To "cut down" thick vegetation, I will use the destroyer (not that it doesn't cut it easily, but for movement from top to bottom, the destroyer is better) and for thick branches (up to 7cm thick), the toothed round discs. For all of the above, I ordered a second one for backup...