I'm extremely pleased with the Acronis module for WHMCS. Once properly configured we're able to allow customers to auto-provision 30 day free trials and upgrade. In the event the client doesn't continue with the trial it's automatically decommissioned. The integration is fantastic and we've got customers online and running with it, without issue. Because no software is perfect I will say the documentation for installing and initially configuring Acronis is difficult to follow but if you've installed and configured an add-on service in WHMCS it's the same.
Thank you for your feedback!