You might consider buying a cheap 7" tablet on Amazon and using that for your dji. Assuming your controller can handle the size. I have an older dji and that's what I do. Nothing of importance on the tablet. I think a Lenovo 7" was like $99 when I got it.
Regardless of company size or popularity, that is sketchy. While not perfect by any means , google play affords some security scanning and privacy awareness info on apps that are published there. Others are probably right. And I bet DJI probably wanted to skip that step to trade for ease of management. But any time you install something off a non play store repo you take on a little extra risk.
From memory there's a fee in order to publish an app the the play store so I would assume they're circumventing that by hosting the app on their own website.
You could also upload the app to virustotal and see what that says if you are concerned.