I use app-arch/p7zip-9.20.1-r4 on Gentoo GNU/Linux (amd64).
p7zip forcely expects windows-type of archives (mixing archiving and compressing in single format).
For traditional Unix types of archives (archiving and compression are divided) it requieres re-run (first decompress, after extract files from archive) 7z utility at the time, when I can make one-step decompression and extraction using tar utility. Also 7zip fails to open archive in filemanager (opening .tar.bz2, together with .tar.gz and .tgz in 7zFM shows not files, but .tar archive).
To my mind, cross-platform utilily must provide complete support of native Unix archive types.