You know, you can just read the man page for 7za. The project is called p7zip (portable 7zip), there's no p7zip command-line tool. And as usual, we recommend cloning a tagged revision to get the source for a release.
I never thought to type "man 7za", which does tell me the difference between 7z and 7za:
7z uses plugins to handle archives, so it might be slightly slower than 7za(1) but can
handle more archive formats.
typing "man p7zip" tells me that it's a wrapper script.
p7zip(1) General Commands Manual p7zip(1)
p7zip - Wrapper on 7-Zip file archiver with high compression ratio
7-Zip is a file archiver supporting 7z (that implements LZMA compression algorithm fea‐
turing very high compression ratio), LZMA2, XZ, ZIP, Zip64, CAB, RAR (if the non-free
p7zip-rar package is installed), ARJ, GZIP, BZIP2, TAR, CPIO, RPM, ISO, most filesystem
images and DEB formats. Compression ratio in the new 7z format is 30-50% better than
ratio in ZIP format.
p7zip is a gzip-like CLI wrapper script for 7-Zip, and handles only the 7z format (the
native format of 7-Zip), internally executing either 7za(1) or 7zr(1) command.
I can see why you'd switch to 7zip if it's 30-50% more compression.
It's just I've never really used 7z files before. I searched ubuntu software for 7zip and I see Xarchiver supports 7z files but it won't open the .exe self extracting file.
P7zip-desktop from ubuntu software will open the .exe file with no trouble.
Ubuntu's Archive Manager doesn't like the .exe file but does like .7z files.