The knot looks to conform to the SF standard of FIH/double FIH, and no, the side tabs don't make you look fat. (Are the trousers fitted with suspender/brace buttons? It's been my experience that trousers without belt loops assume that one would need suspenders/braces. If you're insecure that your trousers will stay at your waist, suspenders would be the way to go.)
Thanks upr_crust for the feedback. The trousers are fitted so that they wouldn't fall down. But as a back up, it does come with side tabs or braces.