Can somebody explain me this

I saw this on amazon a few days back. How can you get extra 1tb for just Rs400 more? Also how reliable is Seagate or should I go for WD? https://preview.redd.it/o7dip0oaz0ke1.jpg?width=720&format=pjpg&auto=webp&s=3fab35bb2c295f608cb883f5b7c8535a3722804c