Have to say I'm impressed. Yes it adds about another half width to the phone but for travelling having that extra battery is nice to have. It elongates the phone a bit, but it's about the length of my old SGS. Very comfortable to hold and type with it on. I would recommend it to anyone looking for an extended battery case.
Sounds similar to the Mophie (sp?) case that we use. Makes the phone a LOT more comfortable to hold and use. My only complaint is that on the Mophie there are LED's along the bottom for charging indicators and they are white and very bright. Not pleasant for the bedside table. Other than that, it's all win, IMO.
I'd probably Mophie it, instead of sending it in for battery or doing it yourself (I ripped apart my BBs all the time but I am a tad hesitant on cracking open my pretty iPhone lol).
At that point you'd be close enough to a upgrade that the mophie would be a better choice, I think.