Kudos for quick and courteous customer service. I would use MMI again...
After a short review of the website, I had thought that by making the sites I wanted to share data on a master and slave, that I could then sync data.
That is not the case. You can indeed create multiple joomla installations, but given the core hacks and the extensions limitations - a slave can only have the exact same extensions as the master - it is not usable for my needs.
But if you don't mind core hacks and can live with slave sites that can only have extensions replicated from the master, then this will do the trick. The installation is well documented and went without any problems.
I rated it as "average" because it does what it says it will do, I should have spent more time researching. I would have rated it higher if the advertising had been more upfront about it being core hacks.
Documentation is sketchy, but not bad. Most importantly, the tool works as advertised, and the support is phenomenal. I highly recommend to everyone.