Freetrade uses the interbank rate for comparison (see below or full quote here), it might be best to check what II are using, I’d be surprised if they use this - they used to charge 1.5-2% when I was with them! I’ve seen they upped their quarterly fee as well recently.
It’s also worth pointing out than Revolut charges this same 0.5% above the interbank rate when someone exchanges over £5k worth of transactions in a month.
“To clarify, we are not charging a 0.5% commission - we are saying that you will get the interbank rate+0.5%. The rates you’ve quoted are the amount that the other brokers charge on top of the rate they get. The two are not straightforward to compare, as they do not typically state the benchmark they use. We felt it was important to be transparent on the FX rate you get against a recognised benchmark.”