The performance of Headless is fast, really really fast. It is much faster than WatiN which is much faster than Microsoft's CUIT.

Anecdotally, we found that WatiN was up to 10 times faster than CUIT (in VS2012). The poor performance of CUIT was the reason for migrating the acceptance test suite over to WatiN.

We have found similar performance gains with Headless over WatiN. In one test suite of 50 tests, WatiN executed the suite in 7:40 minutes while Headless clocked in at 49 seconds. In another test suite of 23 tests, WatiN executed the suite in 4:10 minutes while Headless completed in 19 seconds.

An entire enterprise solution has now been converted from WatiN to Headless with the execution time dropping from 1:04 hours down to just over 7 minutes.

Which test framework is best? Read CUIT vs WatiN vs Headless