Ok - I will add in a little entry field and explanatory message box when I move up to this version.

OpenExchangeRates has 161 rates available so it is hardly any hassle for what you get.

Also, the 'best' polling time varies from exchange to exchange. For instance OpenExchangeRates updates hourly and with 1000 free polls per month it is pointless to poll faster than that.
Is that available on the exchange metadata or will I have to hardcode it ?