I've been running Gaia on my old iPad2 (vintage 2011 or so, WiFi/Cellular enabled, but I never connected it to a US cellular network; in fact it might still have the SIM card from the German phone company in it..) for several years now, replacing a (vintage 2004...) Mac laptop running MacGPSPro. Worked/works fine for tracking, and I keep my trail inventory there. I've also imported trails from .kml files from Google Earth (works, but not the smoothest of operations).
I now have a subscription, it was something like $60 for 5 years, so I can't comment on the issue mentioned above. Sometimes the iPad2 is slow to pick up GPS signals at the start of the day, and I've had to restart it on a few occasions, but that might be more of an issue related to the age of the device rather than Gaia software. Once it has the signal, it's ok unless you're in a really narrow canyon or so.
On a recent road trip from Phoenix to Yellowstone and back, it worked really well as a secondary navigation device when the phone was unhelpful. I had downloaded road maps ahead of the trip, and we essentially used Gaia to show position on the map - not exactly a navigation device (as in plotting/showing/leading you along a route), but I've grown up looking at paper maps, and the position info was essentially what I wanted. Can't comment on the Android stuff since I've kept on drinking the Apple KoolAid since 1989...