To avoid malware and fake "cracked" versions, always download directly from the official domain: www.wudcompress official .com (Note: Search engines sometimes list adware clones).
Uncompressed Wii U game backups, known as .wud (Wii U Disc) files, are fixed at roughly 23.3 GB, regardless of how much actual data they contain. A game like Super Smash Bros. may take up the full space despite only needing a fraction of it for game assets. WudCompress