Synology DS216j - drive selection for RAID1?

Question

Hard disks

Good afternoon.
Available: Synology DS216j and WD Red 6Tb 5400rpm
I would like a stable RAID1 for the safety of important photo data and backups.
1) Question what to take the second disk?
In many places on the Internet, it is recommended to connect as many different disks as possible to RAID1 (different acquisition path, different batch, different manufacturer), for example, I found it here:
https://superuser.com/questions/257892/matched-or-...
However asking a question directly to Synology (a form on their website), I received the following answer:

If you want disks to work together in a RAID, then they must be as similar as possible (size, rpm, etc.). If the disks will work independently of each other, then it does not matter.

2) Is it possible to take a second drive, for example: Seagate IronWolf HDD 6TB 7200rpm 128MB ST6000VN0041
More details: https://hard.rozetka.com.ua/seagate_ironwolf_st600...
4) Whom to believe?
Can you tell me something?