We will likely not offer this in the app again unless things change at the switching scheme side. 
Unfortunately, partial switches are not covered under the same Current Account Switch Guarantee that full switches are. Additionally, we found many situations where the old bank would send out a switch message that did not include the new account information, causing direct debits to be fully cancelled (despite us sending a switch message including the new details).
In some cases, all of this caused people to be fined for non-payment of their bills (that again, weren’t covered under the switching guarantee).
Partial switches are a great idea in theory but in the real world, we found that it caused significantly more trouble for people than just manually moving them would have been. 