There is no such thing as an affordable attitude indicator that works without some extended data. Many use magnetometers, but those don't work without careful installation and calibration. Some use pitot/static, which we also can't have access to in a portable device.
Many of the certified AHRS devices out there use GPS, most notably the AHRS in the Garmin G1000. It requires GPS for full performance. It has the benefit of having other sensors (pitot/static) if the GPS fails, but as mentioned we can't put those in a portable device.
Some AHRS units supposedly don't use anything, but they require minutes on the ground before you can fly with them, so they can't be quickly initialized in the air.
Ultimately, the use of GPS was the only reasonable way to give the world an affordable, portable AHRS that could be turned on in the plane if needed, and used as a backup. We use the latest GPS chipsets with excellent sensitivity, and they have performed admirably in our testing. No technology is perfect, but in our experience the use of GPS is very reliable, and the Dynon D1 is a product we very much believe in and think is safe and useful. We do make sure we are transparent about what requirements our products have to operate so that prospective customers can make informed decisions before purchasing.
Personally, if I'm in an airplane and my main attitude indicator fails, I'd much prefer to have a backup to that device which has a very, very good chance of working, versus no device at all.
