After a major login issue (which I suspect, from trial and error, is ManageWP’s silent dislike of special characters in passwords), I managed to eventually access the interface. Everything looks pretty straightforward and well laid-out, and I especially like the rather informative Performance tool.
All that changed, however, when I went to update a plugin through ManageWP. The update was apparently successful but when I tried accessing my site directly after that, I encountered a code 500 error. As other subdirectories on my domain worked, it was definitely to do with the WordPress installation. I did the standard elimination exercises with ALL plugins (and themes) to no avail, until I was left with no choice but to remove the entire WordPress folder and unzip a new one from scratch – and lo and behold, my site was back online. I then transferred my previous themes and the site still worked.
I don’t know what ManageWP did during the update but it appears it corrupted all my installed plugins, so hereon, I don’t trust it. I won’t award it one star because as said, its other tools are useful. However, for anything that involves direct modification of a site – i.e. updates – I would advise people to do it directly from the WordPress dashboard. While defeating some of the purpose, it also means you’re more in control of access to your installation.