Your answer is a little squirrely, to be honest. I know how banks work.
You're collecting, withholding and pooling money from users. This we know because I'm assuming your algorithm is not set to run at a loss, and when you "average" allowances you create overages by your own admission more often than not. That money is being placed in a bank account, which we also know because it's plastered all over your site.
That bank account will pay interest to the holder, because as you point out so nicely, that's exactly what banks do.
That "holder", by default, is Even. Unless of course you are setting up a bank account for each separate user, in which case the holder could be the user in trust. That seems silly though so let's just go with the fact that the money is yours and you simply redistribute it properly.
Either way, the money is given to the bank so that they can invest/use it. So either they are retaining the extra profit by not paying any interest to Even at all, which seems ridiculously stupid from your point of view, or you are in fact retaining the interest yourselves, which you aren't disclosing. If I were running this, I'd choose the latter because I like to make money. The issue I have is that you are either not aware this is happening or - more than likely - choosing to pretend that we are too stupid to understand this.
let alone the fact that it's a pretty dick thing to do.
It's not a dick thing to do at all unless you actively avoid disclosing it. You're not charging interest for loans so from the customer's point of view, it can be taken as a break even. Of course the SEC might have a different opinion on these matters than I do.
The only way we make money is the subscription cost of using Even
I have trouble understanding a business model that requires 833 customers with significant money under management to barely take in enough for a single salary. (833 * 12 == 10K) Assuming an average income of $3K per month for these users, you'd be managing upwards of $2.5MM every month! Retaining 10% of that 2.5 as "excess overage" you'd be looking at $250K in that pooled account. At 5% interest, you're either giving the bank a windfall of $12,500, or you are keeping it.
We can all do basic back of the napkin math here. There is something about what you are telling us that doesn't jive with presenting a position that you are going to be successful with income limited to $12 per month per user. You either have another source of income or you are in bad, bad shape. We're all assuming the former.