Actpay has been tested by 100s of users over the past 3 years. All the bugs in the system have been corrected as of June 2016.
Actpay will release updates from time to time, but these are for enhancements and not bug fixes. All the calculations have been tested again and again to make sure there are no problems.
You can use Actpay with confidence knowing that all your calculations will be correct.