The only distinguishing feature that i see here is the availability of multiple customer touch points. In addition to web buying, you can now also buys deals over Phone or chat with a person in real time to get good deals. None of the sites that i have seen so far in this category provide these additional touch points. I wonder why no one has so far thought of using SMS as the most preferred touch point for receiving the deals.
However, the biggest challenge i see for these web sites is to convince the retail merchants to sign up for this channel!
See this interesting video on GROUP BUYING from taggle to know more about this concept here