You don't have to investigate the code, but you should.  You should either review it yourself or you can rely on opinions of people who have.

When you buy a stock you should review the finances of the company to determine if it's solvent and a good investment.  If you don't do this yourself you can choose to rely on the opinions of people who have (stock analysts and ratings agencies).

In fact, a cryptocoin analyst service would make perfect sense.  The analyst would review the source code and the promise of each coin and pass that information on to their subscribers.  An accurate cryptocoin version of S&P would have rated this coin an F.