The benefit of the 3rd signature would be that it can stay sealed somewhere for emergencies (your death).
Again, it's 2 of 3. So you can use the 2 signatures in the way you use now and the 3rd is for the case one of the usual signatures gets out of reach.
But who would hold the 3rd co-sign?
If I die (as I have already stated) there is a PoA.
I am leaning more towards a 2 of 3 multisig - but more in case my clients lose their keys or seed words. But that would mean me holding 2 out of the 3 co-signs.
Unless I set up a company specifically for this or have my lawyer be a co-sign for all of my clients too. That way a 2 out of 3 is the best solution maybe.
There's no ideal situation here.
You can do 2-of-2 and hope that your client never loses their key/seed, but if they lose them, the money is gone.
You can do 2-of-3 where you hold two keys (in separate physical locations to prevent compromise) and your client holds one, but this effectively places the funds in your sole custody. That raises liability issues if the funds are ever stolen.
You can do 2-of-3 where you hold one key and your client holds two (in separate physical locations) but again, this opens the possibility that your client has his keys/seeds compromised.
Whatever you do, I would avoid any liability in case things ever go awry. You don't want to be on the hook for a 20 BTC loss.
You could also consider
an institutional custody service like Bitgo. I'm not sure exactly how their setup and pricing works but lots of services use them for multi-sig storage.
Cheers for your response. All your points are valid and its what I have been thinking.
Me holding 2 of his co-signs isn't an issue - it just my mentality of people holding their own keys (one of the major benefits of crypto) is in conflict with this option.
If 1 of 3 co-signs is held on a USB in a safety deposit box - it will never need to be sued unless in an emergency. (if I or my client lose their keys)
2of 3 seems the safest and secure option.
using a third party company would defeat the object I think - that's losing control of your keys even marginally.
The amount of btc bought from January's figures would be 56 BTC and February so far would be 17.5btc so I think I will delay it for another month and play around with various options first, but I think you and others and myself have convinced me 2 or 3 is the way to go.
