Written by them, after I decide to take their installation service.
What we have reviewed tomorrow is a very strange behaviour that can only be caused by some server settings of your ngix server. Unfortunately, we do not have time at this moment to test the add-on on ngix server and to deeply analyze your settings that could cause such issues. Due to this we refunded your payment. You should uninstall both XenCentral Framework and Multisite System from your server. We are sorry the product didn't work for you.
If we'll have ngix server support tested, we'll update you, so if you are interested in product you may purchase it again.
Pros: It seems to mostly work, some features like Xentag need updating to support the latest add-on releases as they don't work today
Cons: Very very very slow support, practically no answers on XF.com and support tickets on their site take a few days to answer if at all. Given the price I expected more from the authors. Hope this will improve in future.
Updated review. I'm still have a few issues with the implementation, but the developer has initiated contact with me including the willingness to log into my site and take a look, that's good service and shows they're working on their product to make it better ... or willing to help a customer out even when it's not their fault.
Does exactly what it says on the tin, and has worked for us flawlessly in production. Updates have been frequent and solid, and I'm yet to run into an extension that would have problems with working with Multisite system.
Even though I haven't run any vigorous testing, Multisite doesn't seem to have a negative effect on performance either.