I haven't used anything FROST-based, but I think I would if I could do it in a way that seems more secure than regular NIP-46, and convenient to use. For it to be more secure than regular NIP-46, I would want to require all shards for signing and keep exclusive control over at least one shard myself. If there isn't anything in the cryptography underlying FROST which makes it inherently less secure than using an unsharded key, it seems that this way of using it would be at least as secure as regular NIP-46. And then on the convenience side, the actual signing would ideally be controlled through an app that sits on my phone and feels generally like Amber, and that app should probably hold one of the shards over which I have exclusive control. I've only taken a cursory glance at FROST, but if there is something that provides this kind of experience or something equivalent, I think I'd try it.