1. Not all the features are fully functional. For example, the product custom fields don't work properly. IF the entered values carry over into the shopping cart (yes, often times they don't), they don't carry over into the checkout process.
2. Their support is slow to respond and sporadic. I payed the $100 for a month of support and reported the issue of the custom fields not working on April 26th. It's now been over 5 weeks and there's no fix. Most of that time I heard nothing from the support team. I would argue that I've only received about 2 to 2.5 weeks of support. I've even set up a test site, at the developers request, with a copy of the live site. For about a week, an attempt was made to correct the issue, which at first seemed to work, but after further testing created more problems. Communication from them would be very helpful and a fix for this problem is critical. Besides my communication with them in their support ticket system, on June 1st I emailed them letting them know how unhappy I was and have not received a response yet.
As I said, this extension has a lot of potential, but the lack of support for known issues nullifies any amount of potential it may possess.
Come on Dioscouri Team! I really want you to succeed!!