Weetabix is 69g CHO per 100g, Weetabix Protein is 62g CHO per 100g. For a two biscuit portion that's 25g vs 26g - so if you're spiking from regular Weetabix, you'll probably find Weetabix Protein no different.
It's a bit of a misnomer. It's slightly ridiculous to brand something made out of wheat as a good source of protein, and the vitamins that are in it, they have to add in, so it's really no different from taking a vitamin tablet.
If it works for you then great, but I'd suggest if you have trouble with carbs and you want more protein and vitamins, simply eating two boiled eggs would deliver more protein and more vitamins for only an additional 10 calories or so.