Didn’t see this and went ahead and posted my own idea Split Transactions which is identical to this. sorry
Split transactions are a must at least for me to move fully to Monzo, only today did I make a purchase where I needed to split the transaction over two categories and couldn’t, while spending on a credit card then paying the card off later may be a “work around” it sure is messy and takes away from the elegance that Monzo brings to the banking experience in my opinion.
Monzo could still use it’s wizardry 
to figure out where I have spent my money, if I swipe at Sainsbury’s 9/10 that is going to be groceries but that one time I went in to get food and flowers isn’t always just groceries so Monzo can still categorize that as Groceries but if I had the option as outlined in my idea linked above to split the transaction after the fact it would make managing that money SO MUCH easier.
Just my two cents. (Up voted)