Yesterday, I was prompted by an Editing News update sent out by @Whatamidoing (WMF) to try out this editor. I'd not done so before, but soon had to disable it.
The first problem related to template alerts continually blocking much of the editing page. I'm pretty active at the Teahouse on English Wikipedia.there, where we have a template to steer users how to ask questions. Having to be manually dismiss this every time soon became very annoying.
The second problem might only be encountered by admins, but it's impossible to go to a previously deleted page and to click the links on the top left of the page to 'View or restore deleted edits' or the 'abuse log' link. Both links are visible, but are greyed out and non-functional.
I realise both issues are not going to be regarded by most users, but I'm afraid I regard them sufficient annoying that I would not want to try using the editor again unless I knew there's a way to avoid them recurring.