Their 'default' order price is a market order that they promise will not clear until after hours or the next day.
https://freetrade.io/order-execution/
This is quite possibly the worst way a retail investor could send in an order.
Isn't this only true for the non-paying users, who are not subscribers of their premium plan? That's probably their entire (freemium) business model. It's the same with Revolut: free users might lose more money in foreign exchange and withdrawal fees, which pushes them to upgrade[1].
Robinhood seems like a better deal.
https://freetrade.io/order-execution/
In the US they would be required to disclose how much they are being compensated for that. I don't know if that is a requirement for the UK so have been unable to magic search term my way to their disclosures.
https://www.fca.org.uk/publication/thematic-reviews/tr14-13....
So for as long as freetrade is UK only I think you can probably assume they aren't receiving payment for order flow.