What is Casa? I had a look through their site, but how does that service work? Is it simply a 'help line' to set up and recover multi-sig that you control yourself... Or do they somehow have a master back up in case you really screw up and lose all your signing devices? 

 Casa is primarily 3 things:

1. A mobile app that makes it easy to manage a multisig wallet
2. A recovery key holder (only 1 of N keys)
3. A security consulting / advisory service