I've tested both the BadElf plug-in GPS (http://bad-elf.com/products/gps/) and the Dual Bluetooth GPS with the iPad/iPhone (http://sportys.com/PilotShop/product/16597) and OzRunways. Both work seamlessly - that is, if you are not getting a good GPS fix from the internal GPS then the (Apple IOS) software chooses the best it can get. That is reflected in the "ERR" field in the GPS HUD in the OzRwy App. Anything around 10-20m is good, When you see 200-400m you are in WiFi or 3G 'GPS assisted' mode (and your auxilliary GPS if being used, is not getting a good signal either). I prefer the Bluetooth version as you can chuck that anywhere in hard GPS placement situations. It comes with a rubber thingy that will stick to almost any console. Battery life is really good (all day). And there is a 12V USB charger included.
Wrt Garmin's, as OzRwy's says, that is 'work in progress'. Lost likely, it will couple NMEA serial out of 'anything' to the iPad/iPhone via WiFi.
In side by side flying of the iPad and Garmin 495/695 over the past year the iPad has never not had a valid GPS signal when the Garmins had good signals - aka headings, bearings, distances, etc. match in all respects. Mind you, that's in an R44. I do understand in a metal enclosed cockpit you might see more problems. One thing that is evident is that the iPad especially, benefitting from the use of more recent GPS chips is that it is way more sensitive than the Garmin 495/496. For example, the iPad will get a a seemingly real fix indoors when the Garmin 495/496 (even with an antenna) will not (although, I will admit, the IOS is very, very crafty and it might just be faking it). Not sure about the 695 as that is fixed in the aircraft. It's a later incarnation so should be better.
Oh, yeh, I've tested the iPad/OzRwys on a recent Lake Eyre trip and it works perfectly well when there is no 3G for miles.
