Unofficial installers frequently contain malware or background miners.
This specific point release (v5.7.3) addressed critical technical issues rather than adding new sound engines, which were introduced earlier in the v5.7 cycle. Improved Startup Speed: Native Instruments Kontakt 5 v5.7.3 incl Patch
Allows developers to create unique user interfaces. Native Instruments Kontakt 5 v5.7.3 incl Patch