When I saw that these strings only cost €1,5 I thought that they would be absolutely useless. However, I was still curious to see if my judgemental attitude towards them was correct, so I bought these and a pair of 10-52.
None of the strings had any rust or other issues, but I can't really judge the overall "build quality" fairly as I have only bought two packs of strings so far.
The first thing I noticed when I slapped them onto a guitar was that I got much worse ringing from headstock (the part of the strings that go from the nut to the tuners) than I usually have with my D'addario strings. I don't know why this is, but I really needed to tape the strings to be able to record anything without them ringing.
Another thing I noticed is that it seems like these strings produce lower output than my regular strings. I guess this could be caused by using thinner core gauge or that they use more nickel than usual (because it's cheaper, I guess), but this is just my own theories. These strings also have bit thinner tone.
The useable lifespan seemed to be around 3-4 weeks at most (if you only play 1-2 hours a day like me). If you play more than this I guess you get around 2 weeks of playability out of them. After that they start sounding quite dull and dead.
I still feel like I can't complain too much about strings that are this cheap. They are definitely better than I expected, but that's only because I didn't even expect them to play at all pretty much.
I could maybe see myself buying a bunch of these just to have as backup if I don't have any other strings to change to, but I wouldn't use them for recording or playing live. They are better suited for just practicing at home or jamming with friends etc. They could be great for beginners who practices a lot and don't have a lot of cash to spend on strings.
All-in-all; I would give them three stars, taking the price in consideration.