Thanks, but what's with 7zz?
From what I understand, it is the standalone executable that handles more formats than 7za, and 7z uses 7zz by default, or 7zz is a maintained successor to 7z but had to be renamed to avoid breaching compatibility. Correct me if I'm wrong.
Looking at the manuals (man 7z, man 7zz), 7zz seems to be have more options than 7z, but with the same options, compression ratios should be the same.