Not fake.
Just a gigantic blunder of their marketing. This can happen only in China, where they have Sn63Pb38 alloys or Sn37Pb63 advertised as electronics solder.

Anyway, I am using Mechanic wires for a very long time and they always deliver. Hxt100, sx862, sd360, I mean, I have all of those product codes in my head, that’s how long I used Mechanic soldering products.

Which is a reason why I contacted them after buying one of those spools marked sbd366 and advertised as Sn42Bi58. I use this composition (more often paste) just to melt it to something that is already soldered to drop the required temperature for desoldering. When mixed with lead alloys, it should be able to drop the melting point of the newly created alloy to bellow 100C.

If it was any other manufacturer, I’d just think to myself “China” and give it up. But I did contact Mechanic Pro AliExpress store - after all, I used several kilos of their stuff and I was never disappointed like with this wire. As already noted - melting point is higher than of 60/40 type alloys.
Also, one weird thing - they advertised the wire as “melting point 210C”, which simply screams one of those Sn99 alloys.

Anyway, after checking, turns out that this wire is not bismuth based at all.

It’s Sn96.5Ag3Cu0.5 or something like that. Which explains a lot. A bit higher price, formation of crystalline structure when solidifying, temperature, looks, everything.

There’s a video on YouTube on Androkavo channel (which has some awesome soldering videos), video title is something like “Mechanic Sn42 Bi58 wire test”, ofc it shows the disappointing behaviour of this wire. In reality, there’s nothing wrong with it, it behaves just like the most expensive copper based solders and silver content is also apparent. Actually, you can compare it with the Electroloy wire of same composition (on the same channel).

The incredible thing is that this video was made in 2018. It took them years to notice this, and they still wouldn’t notice if I hadn’t contacted them.

Just a few days ago.

Solder guys didn’t do anything wrong, they are just making a high quality wire. And obviously, speak no English.

This is on those other guys, the ones who design labels and commercials. Who knows how many refunds they paid because of inadequate expectations they created with this bismuth half a decade blunder.

Edit: btw, the correct information about the alloy is available on AliExpress Mechanic Pro store, and probably only there, all the other sites, places and people are still living in bismuth fantasy