The tension technique shown is much better than just yanking on the line each grommet, one-at-a-time. That causes each grommet to get strained well over what is needed. When you ease off the mainsheet, the grommets will get fairly equal loads. We used to use vise grips and pull as hard as physically possible on each one!

I think the bow in the side bar shown is not nearly excessive. There is no "Official" Hobie tension, but I prefer a TIGHT tramp that will also reduce the overall wear on the boat by keeping the frame tight and square.