Yes, you can plug the USB C cable into a Thunderbolt 3 port on your Mac. You will get 10Gb/sec (USB 3.1 Gen 2 Speed), not 40Gb/s (Thunderbolt 3 speed).

Yes it can write data from 1 card to another or you can even write data from your computer hard drive to a card.

Yes.

Hi Manuel, We have tested our readers on Windows 10 but not on Windows 7 since it is no longer supported by Microsoft. It should work without a problem and if you have more detailed questions contact our support team.

The magnet is designed so that you can attach it to a PC box and assist in not getting it lost or misplaced & so that inserting a card is easier, not requiring 2 hands. I too had concerns placing it close to a typic magnetic hard drive, so I attach it to the base of a nearby desk lamp base. The magnet is reasonably strong but not to an extreme degree. I use iMacs and Macbook Pros so I dont have hard metal case, but if I were to attach it to a PC case, I would very easily feel safe placing it on any area NOT adjacent to the hard drive location. I think a 'reasonably' safe distance would be beyond 4-5 inches, but that's a guess. It is noticeably faster without any doubt.

is much faster

The now-aging USB 2.0 standard can theoretically transfer data at 480mbps (60MBps). The newer USB 3.0 can handle up to 5gbps (640MBps)—over ten times as fast as the 2.0 maximum. How fast can a Mac read or write to a SD card in its SD card slot? Mac notebooks (laptops) use the USB bus to communicate with the SD card slot. They have a maximum speed of up to 480Mbit/s. Mac desktops use the PCIe bus to communicate with the SD card slot. Desktops can transfer data at a faster rate. Check the packaging that came with your SD media to determine the maximum transfer rate that your specific card uses. To determine the maximum transfer speed of your Mac, you can use System Information. Choose Apple () menu About This Mac and then click System Report. If you use a Mac notebook: 1. Select Hardware, then select USB. 2. Select Internal Memory Card Reader and look for the Speed entry. If you use a Mac desktop computer: 1. Select Hardware, then select Card Reader.  2. Look for the Link Speed entry. Computers that use the PCIe bus express their speed as GT/s. Excerpt from: https://support.apple.com/en-us/HT204384

The ProGrade Digital Dual-Slot UHS-II SDXC USB 3.2 Gen 2 Type-C Card Reader can be used with full size SD cards containing footage from the Blackmagic Design Pocket Cinema Camera 4K.