Differences between WD30EZRS, WD30EZRX and WD30EFRX - technical specs?

Hello there,
I’m starting a new thread since I couldn’t find clear description of all these disks.

I have a NAS 1511 Synology with 5 disks of 3TB.
It had initially 5 disks of type WD30EZRS. One of them crashed few months ago and I replaced with WD30EZRX which appeared to have same specs.
–> is that correct ?

Now a 2nd drive needs to be replaced and a colleague of mine has a spare WD30EFRX.
–> can I use it with my NAS without any issues?
–> will it be “compatible” - with similar specs ?

Thanks a lot !
-Exca

here’s the differences between all of them …

http://www.wdc.com/wdproducts/library/other/2579-001028.pdf

Thank you Joey. Exactly what I was looking for.