I suppose it depends what you're wanting. Looking at Brewie it looks like you can only make using their kits, which aren't cheap themselves, but as an all in one fire and forget, it looks easy. The grainfather would give you much more potential to develop your own recipies to what you want, and is almost half the price of the brewie. It's basically a stainless "Brew In A Bag" system, I think. I'll be honest that I've never looked into either system much as they are way, way out of my budget.
I quess the question to ask yourself between both systems is are you wanting ease/convenience, or are you wanting flexibility? I'd imagine that the Grainfather will be much more cost effective per brew for ingredients, maybe £10-£15 per brew, potentially less if buying in bulk, or not making hugely hoppy brews, where the "pads" for the Brewie are €40ish.
quick edit
Actually reading the Brewie site more it looks like you can do more than just their own kits. It looks possibly more advanced and flexible, but ouch at the price!
If you can afford them they both look nice bits of kit. Have fun!