I have never had a conversation with more than one person at the same time and I am afraid that the quality sound would not be ideal (my internet is quite "poor" sometimes). On the other hand, is not it difficult to have a conversation with more than two people not seeing each other?
It is true that the price might be affordable for more people, who such as myself can not spend too much money in something that it is not necessary (I am learning English for pleasure). So, I would be glad if someone told us the experience of being taught in small groups on Skype.