I have had extremely bad experiences with WPMU. I've installed Dashboard, Smush Pro and Hummingbird on several pages.
Shortly after installing Hummingbird, I had problems on some of the pages, wherefore I deactiveted Hummingbird.
Trying to update to WordPress 4.6 was not possible before I deactivated WPMU !!!
Finally, I use Gravity Forms on some of the websites. On one website, for a company having at least 20-25 filled in forms every day, WPMU collapsed one of the forms.
How do I know it's due to WPMU?
For the simple reason, that by disabling WPMU, everythng worked again.
I have not tried only to use Smush Pro withour Dashboard, in order to see if that is ok.
I want to use Smush Pro, but I cannot take the risk again, I'm afraid.
There must a lot of other people having similar problems.
Are you in fact looking in to the problem, and if so, do you have a solution?
I want to know before I take a final decission whether to cancel my membership.
P.S. I did search on Google, and can see previous problem in 2013 with Gravity Form, but it seems there are still problems.