It’s really worth having a look at Thing Explainer as to why this particular constraint can be useful, fun and interesting.
It’s also worth remembering that people on a forum for a bank are going to have, probably, a high base-level understanding than the average man of the street, and the blog post isn’t written for us.
(P.S, if you’re going to criticise a blog post for how it uses words, you should probably make sure you don’t use any incorrect words in your own post…)
maybe fun and interesting as an exercise but I’m not sure it comes across as fun and interesting publicly, or useful.
This is why I personally don’t agree with their approach, I work hard to try and improve my writing and reading (its not perfect), and this ‘simplification’ can look as if its coming across as a little patronising.
Limiting to ‘simple’ language in this experiment I don’t think worked, apart from the fact that it doesn’t seem to actually make much sense, it also seems to suggest that Monzos customers cant be trusted with big people words, or at least that’s what the article makes it look like they believe.
I think @Smsm1 is on the correct approach. There is an opportunity to teach people here rather than treat them like invalids. You can use the full range of English and provide the opportunity to teach people meaning in words for those who might not know without just assuming they don’t know and never will by not using the language.
Yet it’s common to see forum members own up to being unknowledgeable of even the most basic principles of money management.
And it’s difficult to see who else the article would be aimed at. 
You beat me to mentioning that book, the reason XKCD created the online tool in the first place
I have a copy in front of me
Monzo’s tone of voice guidelines regarding selecting the simpler word or wording for an occasion fit well with this, even though this is an extreme example
What is interest?
Something Monzo doesn’t give or wants to charge you for.
Funny as I bet our money goes towards loans and overdrafts as per this blog.
If you really want to know how bank loans work, look no further than the Bank of England itself which explains in the link below that:
“Rather than banks receiving deposits when households save and then lending them out, bank lending creates deposits.” - i.e. new money is created.
If you don’t want to read all of the link above skip to page two under the section “Two misconceptions about money creation” and note that the Bank of England explicitly says that the way in which loans are made is “the reverse of the sequence typically described in textbooks.”
The OP offers a simplified approach to explaining interest. I reckon Monzo will have received the considered feedback they sought.
Difficult to see how the likely audience would could get to grips with the BoE article.
I agree I don’t think it is perfect and there are certain things that can be improved/ tweaked - but some people (I know a few) actually don’t understand interest - so this would without a doubt help them.
Once you start trying to be clearer/ more definitive in your articles - you lose simplicity. I think what could be done is to write it more complex and obtain plain English certification for it.
Either way - it is a first step/draft, lets see where it goes.
I wonder if these guys would approve of that blog (or anything Monzo writes tbh)
I have got so many people to join Monzo for this very reason. SIMPLE TO UNDERSTAND BANK.
A teacher must explain a topic to a classroom full of students on multiple levels to make sure all the students in the class understand. This will be kids who are bright and high achievers, to kids who want to stick pencils up their nose while wearing their pants on their head.
LOVE that you care enough to explain this to your customers. I do not see other banks doing this.
From a business point of view, a pyramid is larger at the bottom for a reason, you will have more people sign up from the bottom because you speak their language.
Pleae keep reaching out to those people. Keep up the good work.
Thank you
Great to hear 
Why say lot word when few word do trick?
Ok the feedback from the forum is that it is too simplistic. It is simplistic you correct. If it’s too simplistic, it is not aimed at you.
If 99% of users already understood this concept before reading it, then it is not aimed at the 99% and will not have an affect on their lives.
But if it helped 1% of Monzo users, around 20,000, then surely that can only be a good thing.
If 99% of Monzo users think it’s to simplistic, then the 99% are financially literate enough to understand that it is aimed at a market for financially illiterate users, of which their could be many academically literate users.
Academical literacy and financial literacy are not necessarily related.
Education starts with the basics.