DATAPUISTOKEMISTI

Depending on why you're encrypting your SSDs it might be acceptable to enable TRIM (aka discard). With this configuration observing raw content on SSDs will reveal which blocks are used and which aren't. Doesn't matter for me, but might not be same for you.

For whatever reason after updating my Intel X25-M G2 SSD to latest firmware (dated 2011) option to do secure erase disappeared. Yes, I know all about tricks of hot plugging disks etc. Secure erasing another identical X25-M G2 on same PC visible as /dev/sdb works fine. One with latest firmware simply no longer supports it which is also confirmed by hdparm -I.