Does anyone use these? I tried to use them, but 7zip won't recognize them as part files. Can anyone help me?

Yes, they're fine for me. Do you have all the parts in one folder and are you clicking on the first part? Have you tried winrar?

You have to change the file names first before you can unzip them. The MTS upload process adds the creator name and a number which is different for any file. Change or remove that number so that only the ending (partx) is different and 7zip should recognize them.