By this, I mean you can use the Bad Elf to receive GPS reading, then connect via bluetooth to your iphone to view with gaia.
My understanding is that the bad elf will be able to get GPS readings in places where the iphone would not... I know on the PCT my iphone's GPS stopping working for most of the Sierras, as well as parts of washington.
Bad Elf GPS Technical Specs:
Fast GPS lock times (45 seconds or less)
2.5 meter accuracy
60,000ft / 18,000m maximum altitude
1000mph / 1,600kph maximum speed
Up to 10Hz position update rate
66-channel MTK GPS chipset
I think the iphone GPS is about 10m accuracy? Not sure of other specs.