I installed this plugin in a number of sites and it seemed to work fine for a while. I didn't even mind paying $50 for the Gold Cart plugin to get the Authorize.net gateway. For a while it worked fine, but I've since had trouble on a number of the sites it's installed on, the most recent being an issue where trying to check out and pay loops you back to the beginning of the checkout process. I even tried reverting to default themes and disabling all other plugins, and I still get the issue. The community support has suggested changing or disabling shipping options, but that hasn't solved anything for me. And speaking of support, it's almost non-existent unless you do pay for an upgrade, and even then there are times I haven't heard back from them. That's not the only issue I've had though. It seems like each time I set it up there's some code tweak that needs to be made i order for the checkout to be functional unless you're using PayPal, which takes you off the site.
I'm always afraid to update this plugin because it seems more often than not that it breaks something. If some of the stores I set up with this plugin didn't have hundreds of items in them, I'd find another solution. I'm just hoping the next update fixes this checkout looping issue.