I flew with a guy who had the original iPad and dongle and it worked fine. Of course it is useless now since Apple changed the connector. The next time they change the connector, you may have something that won’t connect to anything. Also, I don’t think you can charge your iPad when the dongle is plugged in. That could be an issue on long flights.
I’ve used a bluetooth Bad Elf Pro since Foreflight started and it works fine. This is the fourth iPad I’ve used it on so I’m happy I didn’t get the one that connects to the lightning port. I sometimes use it for hiking as well. It still holds a charge and on the rare occasions I don’t have it fully charged, I can plug it into the USB port in the plane.
I’ve been flying with a Stratux lately and I much prefer it over plain GPS. You get ADSB-IN with traffic, weather, and GPS for $10 less than the Bad Elf.
I noticed on their web page that they say it works on iPhone 6 Plus, 6, 5S, 5C, and 5. I think Apple is up to 11 now. It should work on newer models, but it would be worth a call to verify.