You may have find any 7zx compressed file you haven't been able to open because you didn't have the correct program. Here you are the official 7zx file compressor that will help you compress and decompress using 7zx format and more ones.
7zX offers a very good compression ratio, what makes it specially useful if we are compressing big files.
Developers say 7zx usually compresses to 7z format 30-70% better than to zip format, and 2-10% better than most of other zip compatible programs, although in our test the difference wasn't so big it's true it compressed in a better way than zip.
Finally, we have to stand out that it supports tar, zip, gzip, bzip2, UNIX compress, 7z, s7z and various kinds of segmented archives.