Debian on NSA325v2 and NSA310? (no replies)

Hi,

I just found this forum and I read very interesting info.
I need your advice regarding my Zyxel NASs: 1 x NSA325v2 (functional, used daily, with ffp installed) and 1 x NSA310 (functional but shutdown).

Here are my many questions:
- should I try upgrading them to Debian?
- what are the advantages (beside security patches) on using Debian vs factory firmware (+ffp)?
- is it recommended Debian or OpenWRT? I just learned here is such alternative
- is the performance affected when running Debian? Now my NAS is used just for storage and rarely with Transmission
- what will happen with the data I have on HDDs? I remember something about not being recognized
- can I perform the change using a blank HDD and later one to plug the existing ones?
- are important differences between 310 and 325 when doing the change to Debian? I am thinking to start with 310 to learn and only after to move on 325.
- what would be the topics on this forum to read carefully before?
- what else I must consider before? I have USB-serial adapter

Thank you!