Vanguard Total Stock Market has a yield of 2.14%. Both the long-term gains (when you sell) and the yield are taxed at lower rates (for 25% bracket, at 15% rate). So paying 0.3% now (2.14% yield at 15%), and 15% of gains later. For the same investor in Lending Club, the interest is taxed at 25%. So notes paying 6% interest would result in 1.5% tax each year.
If you had to locate one of Vanguard Total Stock Market or Lending Club notes in taxable, the Vanguard Total Market fund seems much more tax efficient to have in taxable.