Hardbundle means that the discs are already installed, whereas with the softbundle the discs are delivered separately and you still have to install them.

However, I would advise against buying a NAS that only has two drive bays. Later expansion is not possible and Ricardo and Tutti are full of NASs with only two drive bays.

You also give away 50% of the capacity with a NAS with 2 drives. A later expansion can only be done by exchanging both disks.

It therefore makes more sense to buy a NAS with 4 drive bays, the extra cost is not very high. A better solution would be, for example, to buy this NAS with 4 drive bays and then equip it with smaller disks. This way you only lose a third of the capacity and if you want to expand it again, there would still be a drive bay available for expansion:

Synology DS420+ (0 TB)

Combined with 3 x 2 TB, you would then also have 4TB gross, but you only lose 2 TB for the parity information (RAID5 vs RAID1 in the 2 bay NAS).

If a disc should break now, it is enough to simply buy another cheap 2TB disc.

WD Red Plus (2 TB, 3.5", CMR)