The disk manufacturer gives you enough details about what the disk implements, and guarantees the wiping (preferably contractually). Therefore, if you want to be sure about the wiping out of the data, there are only two ways: These "details" are very important for security, and you cannot test for them. Moreover, the key generation may be botched it is possible that the underlying PRNG is quite weak, and the key would be amenable to exhaustive search. If the firmware simply implements ECB, then identical blocks of plaintext will leak, as is usually illustrated by the penguin picture. Disk encryption is not an easy task, since it must be secure and yet support random access. One must note that the encryption-based secure erase really wipes the data only to the extent of the quality of the encryption and key generation. (There is no difference between Linux distributions in that area they all use the same hdparm utility.) For instance, if the disk above has size 1 terabyte and offers 100 MB/s write bandwidth, then 168 minutes are enough for a single overwrite, not the three or more passes that "enhanced secure erase" is supposed to entail.
In fact, when an SSD implements "secure erase", it MUST use the encryption mechanism, because the "overwrite with zeros" makes a lot less sense, given the behaviour of Flash cells and the heavy remapping / error correcting code layers used in SSDs. This strategy is applicable to both spinning disks and SSD.