The video is perfect with the extender. The video quality has to do more with your WiFi signal rather than the app.
I've bought one but DJI have it at 10-15 days delivery (n)
Definite improvement using the WiFi extender along with max bitrate.
Slow Mode https://photos.app.goo.gl/3aUx5mLzfBFiEP9s2
Fast Mode https://photos.app.goo.gl/XEbk3Pfvem0QmM9N2