If you copy a FlexGroup from a Modular Website to a Freeform (Conventional) website, you retain the FlexGroup functionality but lose the toolbar.
I am sure Xara can re-implement this.

Do not just drop a Web Block onto a conventional website design; Xara zaps out all the new functionality.

Without the toolbar, you cannot adjust the Flex Layout (toolbar values).
Instead you have to pick what you want in advance.

Next you select the FlexGroup and apply a Push to it and all other objects on the page.
The page bottom extends or decreases automatically.
Objects can be added, removed and rearranged.
Push can be switched off while passing a FlexGroup over another and then re-applied (Shift+Ctrl+H). Not as slick as a Web Block.

All without the need for a Variant.
Yes, you can include a Variant but you can now re-arrange the FlexGroups as you choose, adding or removing FlexGroups and enwrapped objects at will.

Sadly, pasting into a non-Plus application loses the FlexGroup capability so not block work for Magix software. Not checked for the Perpetual version.

@Xara - With the inclusion of the Flex Layout, 95% of current functionality in a traditional design is achieved.

Acorn