I have been following these developers since beginning. Their support is excellent. You just contact them and they help you without asking to know you have a active subscription or not. Email, forum, ticket support, everything is fast, they often reply my email in just 15 minutes. Just visit their forum, you will see what I mean here.
CMGroupBuying, I am very happy with it. Easy to use, useful features and the most thing I love is it has a new version every month, new features are from users's requests. The developers never ask us for customization project. Just ask them new features, they will develop them in new releases for FREE!
I agree with most people here. These kinds of developers are really rare.
This is my first review on this website, and I do it as a thank to developers. Thank you for a great service! You make me love Joomla and its community!