Is it possible to optionally use it as a single sig device, in similar way like it's possible with Seed Signer device in settings?
Multi sig has many advantage but sometimes you want to avoid complications for whatever reason.
I have just added support for single-key wallets. After entering your mnemonic, you will be presented with a new screen asking if you want "Single-key" or "Multisig" before landing on the home menu. Note that you still need to use the coordinator software to create the single-key wallet and generate PSBTs for you; Krux continues to act only as a signer.
You'll want to pull down the latest code and do a full run through the steps: building the firmware, flashing the firmware, building the software (new step), and flashing the software.
If you run into any problems, feel free to file an issue on the repo or drop a message here. I'll try to check in on this thread more frequently.