Most flexible plugin for purchase restrictions

The free version is a bit poor, but the pro version is much cheaper than similar plugins and it does everything others do and more. I needed it to sell multiple wine bottles in packs of 6, and this plugin is the only one that allows grouping within a product category. Also, I had to contact support because I had a small bug and they sent me a patched version of the plugin in less than 24h. So 5 stars for the support!