Another day, another unicorn public offering. Today it’s Acorns, a consumer fintech service that blends saving and investing into a freemium product. It’s a company that TechCrunch has covered extensively since its birth, including through the pandemic’s impact on its business, both good and bad. The Exchange explores startups, markets and money. Read it every morning on Extra Crunch or get The Exchange newsletter every Saturday. Acorns fits inside the larger savings-and-investing boom seen over the last four or five quarters as consumers buffeted by the economic changes brought on…