The battle has raged a long time between useful, inexpensive, portable, non-certified devices and panel-mount certified instrumentation. In practice, we’ve long used non-certified portables for navigation and we haven’t been falling out of sky in swarms.
Officially, our non-certified portables are for advisory and supplementary use only. In reality, though, if you don’t have a GPS in your panel allowing you to fly direct for hundreds of miles, you can still use a portable GPS. To be legal, you get a heading and “direct when able.” It’s an official wink and a nod, and it works.
