What's the craique nowerdays ref GPS/trackers?

Raced a lot 20 yrs ago and getting back into fell running. And I'm used to tracking all my training with a tracker/smart phone etc...

Back in the day , fitness trackers and GPS watches and the like didn't really exist - but basic handheld GPS units were just starting to emerge.

For fell races there was never a mention about them.

For Mountian Marathons, navigational challenge events etc..... there was an explicit instruction that you couldn't have them, for obvious reasons. But altimeters were allowed.

So what's the craique nower days?