Service was exemplory, from drop off to airport terminal to pickup and car valet. I've used Masterpark (lot B and lot C when it still was Masterpark) for about 4 years now. No issues with using Groupon, just open the voucher in the app and present the voucher.
They were flexible with my return time as my flight was rebooked and it still fell within the return window so there were no extra charges. I highly recommend.