if you need a lot of flash power, best to point flash head directly at subject, with a diffuser.
Bounce card probably requires more flash power, which your 430EX might not be able to provide for an outdoor shoot.
Like what Bro ZCA mentioned, Ur flashgun might not have enough power to provide for if subject to cam distance is a concern (far). Any nearer workign distance it should be fine.
Normally for outdoor shot i have a demb flip it pro on top of my flashgun always (either as fill light or main source of illumination)