One problem I had with a previous quad was how much it dropped GPS while flying.... is this dual gps claim in the videos something that will make fly away's a thing of the past??
Nothing can make fly-aways a thing of the past or an impossibility.
What dual GPS, dual IMU and dual Magnetometer (compass) can give you is redundancy so that potentially things are more reliable since if one fails you have a back up.
Although dual GPS is not really to do with preventing fly-aways, it is simply used for better positional accuracy.
Now for the price point DJI cannot give true redundancy which requires three of each module. That way a comparison can be made between each of the three and if one starts giving differing data to the other two it can be switched out the system by the flight controller and all is well. With only having two of each sensor, if one gives some strange data there is no real way of knowing which of the two is feeding the erroneous information to the flight controller. So, no, dual modules DOES NOT mean no more fly-aways. However, DJI would have written in algorithms to the flight controller that will look at the data coming from the accelerometers and gyros whilst comparing the attitude of the aircraft with correlation to stick input. If the two do not agree, the erroneous IMU would be ignored.
Having said that, the Mavic (like the Inspire and
P4) utilises both the Navstar constellation (GPS) and Glonass to give a better HDOP/VDOP accuracy and thus better positional hold.
Altitude information can still be utter rubbish utilising GPS data which is why the barometer is used for altitude hold. The solid state barometers used have a resolution of around 10cm so are pretty accurate (but can still fail)
To date, no manufacturer (including DJI) have built a platform that has no single point of failure - they will come but as yet nobody has achieved it (and certainly impossible on a quad)!