I've just spent the last several weeks building a large (700+ items) online store with Tienda. My client and I ran across some bugs and some "undocumented features," so we paid the $99 for a one-month support subscription. The service we got for that $99 was OUTSTANDING - the developer spent many, many hours handling bug fixes and even implementing feature requests. I'm not sure what happened with the previous reviewer's support subscription, but I was very surprised to hear him say that it was a rip-off. I got extensive one-to-one support from the owner of the company; you can't get better than that. I would suggest writing to the Dioscouri team again, politely.
I will admit that Tienda is still in its infancy; there are features that some people would consider essential that are not yet included. But you can always install the free version and test it out to see if anything that's important to you is missing.
Tienda is VERY intuitive to use - for shop customers, for shop owners who aren't technical people, and for site administrators. The built-in styles are very nice, but it's also easy to style if you're a designer who's good with CSS.
I'm willing to bet that within a year, Tienda will be the Akeeba Backup of shopping cart extensions - it has the perfect balance of simplicity and power, and best of all, it's free.