I have tried many systems in the past, and so far this deal it is by far the most generous offering at the moment.
I setup my website builder services on my own domain as the services offering website, that was a piece of cake. The domain i setup for the agency is the same, but the system will use my own domain for the whitelabelling bit, so when i prepare a website and need to show clients, they will see my company only. All very quick to setup.

Pros:
The dashboard is very clean and easy to use which allows me to see all client websites, i can add users to the CMS of each site and they see my logo if the are in the CMS. Whats even better, is that you can make comments and the client can write there own as well, making the process easy.

The actual builder is easy to use, and if you are used to other builders you will feel at home. The difference with webwave, is that elements can be placed wherever you want them to go, so you are not restricted to a column system. It seems to have all the features you will need.

The features for agencies are incredible, you will not find any other platform that can offer the same deal, so this Appsumo offer for that alone is worth 5 tacos.

Been around along time, so confident in the support and new features being added

To add on websites will not cost much, so big margins can be made

Cons: (Maybe some of these have been addressed already):
UX is a little dated, but does not mean the functionality is limited.
Would like to see a funnel system
Would be nice to create landing pages for clients on a subdomain that does not use another website credit.
This is personal, but it would be nice to have Payfast so i can sell in South African Rands (a south african gateway added to the mix for the ecomm side)

All in all, Webwave deserves 5 tacos for the very generous offer