Name Generator: what is the difference between the two list types?

What is the difference between Name Generator’s “Name List” and “Legacy Name List” (see bottom right on the screenshot below), pls? Also, will it influence creation of a user name list?

User manual deals with this tool in section 20.4, specifically 20.4.2, but it does not describe the difference between the two options.
The difference is hinted at in this thread (Name Generator - #9 by LAP), but not enough to appease my puzzlement.
Many thanks in advance for any kind help!