recently switched a joint account from Monzo to Santander, and this closed my Monzo account. Yes, it was for the switchers cash. I wish i had used a donor account to switch. 
But … i’m struggling with the santander app. the main thing i miss from monzo is the “tomorrow’s” payments showing in the account feed - telling me a DD was coming out ‘tomorrow’ and also the amount (not a view of upcoming payments based on last month’s amount).
I still have a personal monzo account, so tried to open a joint account again, but no dice. They “cant offer me a joint account right now”. 
I dont want to go with Starling (use them for business already), and from looking around, HSBC are the only main bank to offer a similar tomorrow’s payments app feature - and a joint account.
Think I may shift the direct debits back to my personal monzo account, and just forgo a new joint account.
And ‘try before i buy next time!’.