Have you tried Tap Signer or Cold Card MK4 with Nunchuk NFC tap? Should work like a charm. I have not tried Nunchuk NFC with my MK4 yet, because I scratched off the NFC connection on the PCB and it’s got NFC physically disabled. I do have a Tap Signer and can confirm that it works very well with Nunchuk, whether in a single sig configuration or a multi-sig configuration. My assumption is that the MK4 will work similarly well, since it’s based on the same spec.

When you’re using the Ledger, I assume it pairs to the phone via Bluetooth? I’m quite skeptical with hardware wallets having Bluetooth support, because of the range of Bluetooth, it seems like a bigger attack surface.

I remember listening to Craig on a podcast getting asked about if he will create a mobile version for Sparrow, and he said he wants to focus on desktop now and has no intention to work on a mobile phone Sparrow app. He may or may not have change his mind since the interview, but don’t count on a Sparrow phone app anytime soon.