Apsona's code includes significant emphasis on minimizing Apsona's API usage. It is of course natural that heavy usage of Apsona implies larger API consumption. But in practice, we have had virtually no issues from any of our users on API consumption.You can get an idea of overall API usage via the API usage report in Salesforce, available via Reports - Administrative Reports - API Calls Within Last 7 Days. And you can also get an idea of Apsona's API usage by looking at the little "usage report" at the bottom of the Apsona screen (see screen shot at left). The number shown there is updated every 5 seconds, but only based on the last request that Apsona made to Salesforce. So if you are actively clicking around in Apsona, you will see the number change every so often, but the Apsona screen is unused, that number will not change.