Sorry for my late answer.
I had no bad experience so far from using the testmode other then sometimes it needs a reset, i installed many other apps and games etc so it's not 100% stable
If i take the memory card out and press reset it all goes back to the old navigation from pioneer and that still seems to work. Everything like the new gps software and apps are on the memory card so no changes were made to the original software.
Wich Avic do you have ? if there is a testmode for it it should be on this forum.