I’m just a bit curious about how Monzo decides how a feature is going to be rolled out. There doesn’t seem to be any consistency. This isn’t a critisism, just genuinely curious. To demonstrate what I mean, these are some of the features that have been rolled out lately, by different methods:
Features that rolled out for everyone - Category budgets
Features in labs - EAS pots, safety nets, pre-approved transfers
Opt in through a form - Physical Flex cards, change Flex payment date
It’s all to do with testing. And acceptance. No need to open up to the masses if (a) it screws the servers (b) no-one wants it anyway.
Personally, I like the way 
rolls out testing.
Most things are rolled out in stages by a percentage of the overall customer base each time.
Never really fixed or identifiable in their method (unless it’s something specific, say Premium/Flex customers only).
The percentage also depends on the scale of the project.
If I got all the new things on announcement day, I would too!
But I don’t, so I hate it.
I generally prefer things that just ship for everyone. I don’t like staggered things.
I’m learning google do things the Monzo way too as I’m impatiently waiting for my Google Home app to get the update that shipped with the latest app update but is only being turned on gradually. The app notes said over the next few days but it’s been longer than a few now!
Probably because you don’t work in the customer service team and have to answer one million questions about a new feature every time it rolls out 
For the OP question, I think Monzo have written before about their structure which allows different teams to ship things relatively independently so on that basis I guess it’s down to the team. With spending categories, they probably had all the feedback / input they needed from Summaries which was a very similar thing. And also I would think less worried it would interfere with something critical like a payment process.
I would want to see an updated article on this too! I actually like how Monzo chooses to rollout, it seems to work well and be based on logical ways to get the features out to users at a sustainable pace.
I’ll see what we can do!
It’s worth stating that every Monzo feature is rolled out to staff first who test it in everyday life 
