Former Hamburger Today editor Matt Jacobs checks out two of Park Slope’s newest burger competitors for Metromix today, and the hamburger horizon doesn’t look bright for Slopies. Neither Brooklyn Flipsters’ nor Corner Burger’s offerings stacked up against old diner-standby Bonnie’s sirloin burger, even though the latter is shockingly served on a Kaiser roll. Flipsters was a close second, thanks to daily ground-beef deliveries from Master Purveyors, but a medium-rare order turned up closer to well-done, and the house burger’s toppings — bacon, mozzarella, and caramelized onions — are misguided. Corner Burger fared worse, despite Jacobs regretting having “to lay the smackdown on a nice lady” owner who was so chatty she volunteered that her tasteless, overground beef comes à la Costco. A word to rookie restaurateurs: Bloggers are everywhere.