I personally use the Mini to Micro ones (exactly like those) to charge my N900 from my old Motorola RAZR charger (RAZR used a mini usb port).

They are, to say the least, fragile. A little bit of force up or down when it's attached to another port, and it has a high chance of pushing itself open from the inside. Inside the cords hold together, and if the pins that hold the two plastic pieces together don't break and you don't damage the actual cord bits inside, you can just close it again. Applying tape or maybe glue to where the two plastic parts come together on that adapted would probably solve this. Careful use makes them last for a while too. (I just noticed the pictures are different for that product. The first one shows different ones than the second two... So *Shrug*. My experience is with the one shown in the generic first photo.)

As for the first item, the USB to Mini USB cable, *shrug* should work, with the other one.

Assuming both sellers are legitimate and you get both of them as advertised and working, I would say it should be fine.