Yeah, that was my number one concern - warranty.Yes this is a logical well thought out approach. It is your Phantom. If you are flying it and a crash occurs that is related to a third party app it is reasonable to assume you are completely on your own or at the mercy of the developer of the third party app. So if you are more adventurous and decide to do that... go for it.
My .02 this isn't about the reliability of any of the 3rd party applications versus DJI GO. This is about flying within the constraints of the warranty. I think it is reasonable to believe that you are more likely to get warranty repairs done if you are flying your AC with DJI software.
Just my .02
UK