[wb8yst]

The 3rd party apps work well after getting it set up (above).
I just change the comm and the baud for my BT iBlue 737 Pro
and can switch between internal and external GPS.

Have no trouble using both on PocketFMS, iGuidence 4.0, Topo USA.
If I am splitting hairs for vertical NAV I use the BT iBlue 737 pro -
updates up to 5 times a sec where the internal is once a sec.