It is not worth investing in a article spinner. If you want to save your own time in producing the content or articles, consider hiring writers that are able to write original, authentic and useful content.
And by the way, there is no minimum originality index. Spun articles usually take out the authenticity or the tone behind the article and some parts of it may not connect with the rest. Instead of judging the quality and "rankability" of your article by hard metrics such as minimum originality index or keyword density, why not spend time in crafting a useful or interesting article that people will actually benefit from by reading it?