You need two of those! One that allows expansion, the other to let air in from use driving down the road.
Trust me, if you cork up a 240's tank with all new hoses and a properly functioning cap driving down the road with a Holley Blue supplying fuel to the Webers you get a mysterious "no fuel pressure" problem after about 45 minutes on the freeway, and when you open the hatch, you fund the plastic filler neck sucked FLAT because someone capped the diverter valve on the left fender well with a couple of black vacuum caps!
I converted all of my fittings to 10mm, and used fuel line to preserve full function of the EVAP system, when you pressurize the tank by plugging the diverter valve it will hold 3psi for days!