Thanks, it works and it took about 6h to sync. The wallet is good looking. Exploring the settings I saved the seed and created a spending password as I would do on the real network. I'm confused by the backup part, the instructions say that the seed isn't enough to recreate the account but you need other settings too but it doesn't say which ones or how to save them (I don't remember the exact phrase because it was deleted along the seed after I saved it).
I agree with this assessment - I think clearer instructions on how to backup the wallet are necessary.
You need to back up the entire data folder (~/.config/Byteball test on linux). This folder includes private payments (blackbytes) which are not restorable from the seed.
A better way to prepare for the device loss or failure, is by setting up a multi-sig wallet with redundancy, then you'll automatically have several copies of private payments on multiple devices.