Got my Mugen battery yesterday, first of all. im really impressed by the battery. (so far) much better than the original one.
And the size of the phone is not really an issue, still fits perfectly in my pocket. and to be honest, its much more comfy typing with now. You just have to get used to it being thicker, so after a good week i guess i wont notice the thickness. Not sure if there are any belt pockets for it with the mugen battery though. Why not put it in your pantpocket.
Also , my old battery (stock) was at 84 % from 6 in the morning, to 8 in the morning, from 97%. Mugen was at 97% at 6 in the morning and 94 when i got to work. And this with some sms's.

Kind regards,
Futtawuh