Robinhood says 301,573 users participated in its IPO, representing about 1.3% of its 22.5M funded accounts as of June 30 (Marie Beaudette/Wall Street Journal)

 Marie Beaudette / Wall Street Journal: Robinhood says 301,573 users participated in its IPO, representing about 1.3% of its 22.5M funded accounts as of June 30  —  Buyers represented about 1.3% of the online brokerage’s...