from what I can work out it is more expensive when using non ionity chargers. Ionity is meant to be cheaper but on on the free service.
Another forum discussed this and people are recommending... if you use ionity a lot, charge via wecharge on a premium service. WeCharge Go 45p as opposed to 69p but to justify the £6 per month that means at least 25kWhs per month to make a saving. But we are talking about pennies. When you are talking about 100kWh every month it might then be worth the effort and fee.
In reality just set up the common ones which are on your route... BP, Shell, Ionity, Osprey, chargemaster, ecotricity etc. Its a few hours one night to set these up on your phone, but once done you are covered.
shows a chart of the market share of the RAPID chargers (not the first one with destination charge points)... if you use their map and filter by options such as the supplier, then you can see who is on your typical route.
Also zap pay... which is payg at the rate of the provider... seems a simpified way to use a few chargepoints with a single app.