I sat on this deal for a while before stacking two codes. While I was initially on the fence, their willingness to listen to Sumolings and implement much wanted features like CNAME, Stripe, and eliminating the limit on active students made me buy. I also like how promptly the Classtra team responds to questions. Would still very much like to see some features like Whiteboard, Live polling, Breakout rooms, and sub-institutes, as well as the ability to lock student mics and cam (so that they are not accidentally turning them on during a class etc.), and the ability to add/customize our own terms and conditions. As they have promised that many of these features will be implemented within the next 3-4 months and since they have made good on their previous promises to us Sumolings (eg. CNAME and Stripe), I have decided to take a chance on them.
Planning to stack a few more codes to use for my own academy later (once the additional bells and whistles are implemented as promised), but in the meantime, I plan to use the current codes to help set up online classes for some schools and teachers in my hometown who could use a hand with remote education.

I'd rate Classtra as follows:
For the vision and commitment of Classtra team: 6 tacos
For the product itself: 4 tacos
For implementation of road map items and listening to feedback: 4.5 tacos
Overall, I'd say 4.5 tacos, but I'm going to round it up to 5 tacos.

One recommendation, as Eugene_Spivak (and many others) have already suggested is, please don't limit or lock yourselves to being a "Live Only" platform. We understand that it's your model, but please also consider providing native integrations which educators can use to conduct some recorded classes or hybrid formats with recorded and live sessions (like students can watch a video, but then another session could be conducted to answer questions about the recorded video). And Zapier is a money pit and most Sumolings enjoy having integrations where they don't have to pay a recurring monthly fee (I guess that's why we all love the LTDs here on AppSumo ;) ) You don't have to provide the infrastructure to host the recorded videos etc, but just provide integrations to services that do and it will go a long way to help you compete better without compromising on your "Live Class First" model. After all, adaptability often wins over rigidity. :)