Nice concept. Thanks for taking the time to put it together! 
As far as I know, the design team at Monzo aren’t massively keen on pie charts, as per a post by Hugo on the pros and cons.
https://community.monzo.com/t/where-are-the-doughnuts/5904/2?u=tomsr
As @Rat_au_van says there are some big changes coming to the way our spending data is shown. And some of it will certainly be circular - particularly when showing us how we’re getting on with our monthly spends.
