Thanks for you using both GH-601 and GH-615.
Not only shape different on GH-615 and GH-625.
The battery for B type is 750mAhr, and M type is 650mAhr.
The major difference is user interface likes Lap, Custom Page, Smart TrackBack,..etc.
And you update from GH-615 to GH-625 by firmware upgrading.