Re: What can a user do ? Use multiple devices ?
The triplication system requires a polling system - i.e if Phone C returns a different answer to the other two, you can hazard a guess that C is wrong and A and B are okay.
If you simply have three different phones, say iOS running on Apple and Intel hardware, Android running on Qualcomm, and BBOS running on Broadcom, then you run the risk of giving an attacker more attack vectors if each phone has access to your email or banking services.
Of course you could have multiple phones, each one only turned on for a specific use. It wouldn't be impractical to have your main bank account tied to one phone, which you keep at home in a safe. Your out and about phone would have access to your secondary back account, which would only contain enough funds for each day - limiting how much a miscreant could take.