Here's a pic of the two side-by-side. As I said, I don't really consider the NX to be substantially larger than the TK.
I didn't take photos in all three dimensions, but I have the belt clip on the back of both radios and they are equal in depth. The actual body of the radio is maybe 6-7 millimeters bigger but the NX belt clip is flatter and makes the radio pretty much the same size.
Width and height wise you can see from the photo, if there are any differences, it's in the millimeters - IMO not enough to worry about.
The NX does feel heavier by a few grams to me, but again, nowhere near enough to be a concern.