Sander How does bunq calculate savings? To calculate savings, they need to have a amount to compare to.
As there is much competition on the international currency market, the costs differ per provider as do the costs of handling currency conversion at banks.
So you would save at bunq, but how much and compared to what? The most expensive currency service or rather the cheapest service on the market?
That being said it is rather irrelevant to state the amount you have saved. When the most expensive service charges 15% I have saved 15%, but compared to a mainstream bank, which typically charges (say) 3%, I've only saved 3%. That bank could argue that you saved 12pct, which is much more than the 3% bunq could state. So the mainstream bank gives you much more value as they save you a whopping 12pct.
When bunq tells you it saves you 15%, they are being honest, but not realistic as the average costs are lower. So the question is compared to what you save.
All together bunq could suffice with the statement you have chosen the cheapest option by using ZeroFX. Stating the exact amount of savings is a farce as you can't compare to any price in the market as they fluctuate and there is always a cheaper alternative (except for ZeroFX off course).