My only worry with this mod is why DJI didn't do it themselves in the first place? When the Phantom was being developed they were already mass producuing 'all in one' GPS pucks so creating the leg mounted compass just for the Phantom would have added to production costs due to the need for bespoke circuit boards, cables, compasses and mounting brackets. From a pricing perspective that doesn't makes a lick of sense unless they had experianced a known issues using the pre-existing all in one board under the plastic shell when they were testing?
It does look cool like that with no legs... personally if I were to do it i'd want to poke it out of the top of the shell on a small pole just to be safe but then I'd likely do the 450 conversion if my GPS packed up anyway.