Two different goals, not two competing tests
Sakinorva is a free typology test best known for reporting your result through cognitive function lenses (Ni / Ne / Si / Se / Ti / Te / Fi / Fe) rather than only as a four-letter type. It is widely used by readers who already follow MBTI deeply and want to see how their answers map across multiple typological frameworks at once.
MBTI USA is built for the opposite reader: someone who wants a quick, classic four-letter MBTI result without first having to learn what the eight cognitive functions are.