If you have a straight run, awesome. No need to use elbows. Less corners the better flow and efficiency. Their is a limit on the number of turns you can make before you create a fire hazard. So two is about the max. Distance is also an concern. They probably have a kit that does not have elbows but, because they installers have to decide on site they recommend this kit. Overkill in your situation. But, rare in today’s cookie cutter homes.