Keith, a basic reading of the articles on the site you just sourced is consistently anti-Clinton. That makes it hard for me to take the criticism serious. As you've already noted, it isn't "mainstream." And that is the problem with both Bernie and Trump. The past record of presidential elections is that mainstream people get elected far right and far left folks don't.
Trump is hard to predict because no one really has any idea as to his real positions on anything. Clinton is has been consistently a middle of the road Democrat.
It seems pretty likely to me that the ticket will be Clinton against Trump. The numbers for Bernie aren't good. So are progressives going to tear down Clinton and naively give the election to The Donald? The possibility worries me.