Dinshaw,
There are actually several AD-AHRS units that are compatible with the iFly 720. Actually, when we can get our hands on one of the new Stratus, we will likely confirm compatibility, as we are compatible with the old Stratus. Other manufacturers like the iLevil and Clarity Dual SV would be some great options, as they will be compatible with the iFly 720 and other apps like WingX and FlyQ. Appareo, seems to be focused on exclusive hardware to Sporty's and ForeFlight.
I will say the iLevil and Clarity offer great products. The iLevil has about the best AHRS we've seen and the Clarity Dual SV offers dual band traffic, bothe 978 and 1090. You can't go wrong with either of these and you'll likely have more device/app options down the road. I hope this if of help.