Extreme transforms can distort outlines or spacing
Monospace forces equal widths (can change rhythm)
Flip/invert can stress hinting in some families
Height extends beyond ttf boundaries at certain values
Limits keep TTFs reliable across apps
Why these fonts are free
Google Fonts hosts open-licensed families (often SIL Open Font License or Apache 2.0). These allow personal/commercial use and modification. These fonts and any modifications you make to them are 100% free-to-use :)