i m using acymailing 5 for years, but now finally using acymailing 6 for a client. it looks pretty solid!
for the content-blocks, will there be also a content for flexicontent? that would be very usefull.
There's an add-on for Flexicontent, you just need it to add to your install.
Go to Acymaiing->Add-ons and switch to the tab Available add-ons. Click on Download and it will add itself to your Acymailing. Here's the documentation of the add-on: https://docs.acymailing.com/addons/joomla-add-ons/flexicontent