I eat weetbix with an extra 1/3cup of Bran Plus. No probs for me.
My advise thou - what ever option you do, work up gradually. For me, once my tum was up to eating that sorta stuff for breaky (m/s ment the only thing i could mostly hold down was vege on toast) but, the first time i had weetbix with bran - spent most of the day on the loo! So, i just had plain weetbix for about a week, and then gradually added a bit of bran every day.