I may be missing something here, but your platform seems to only display offer. That’s fine when placing new buys, but although the offer price is reflected in the portfolio value, I can’t easily see the bid price.
I haven’t sold anything yet, I assume the bid price is shown when you sell.
I know you major on this free end-of-day filling (including sells presumably) but every broker shows bid/offer, and therefore people can see the spread. It will matter a lot if you move into smaller cap stocks, where the spreads move with liquidity.
Anyway, I predict that in time, the bulk of your business (in size terms, not trades) will be the paid instant variety.