I'm a native user of Kannada. A PDF of review of Noto Serif Kannada(only design issues) is attached.
Also when were Serif fonts for major Indic scripts released, according to https://github.com/googlei18n/noto-fonts/tree/master/hinted they were updated 7 months ago
These aren't reflected in https://www.google.com/get/noto/updates/
Noto Serif Kannada Review.pdf