It does add bulk, but less than I would have expected. What I really like about the Nillkin TPU case:
+ Its very nice to hold due to the texture on the sides
+ Its easy to slip in and out of your pocket, yet its still pretty flexible
+ The cutouts are perfect
+ No problem using the keys, they still *click* on press
+ The part thats slips around the bezel of the phone is quite thin (compared to other tpu cases), keeping the phone itself, when layed out face down, protected against sand etc. but doesn't add unnecessary bulk.
I guess TPU cases get better as they go as this one is the best Ive used so far
Hop this helps someone!