Just posted:
Canon RF 1.4x Extender Review.
I plan to update these reviews when higher-performing compatible RF lens models become available.
The Canon RF 1.4x Extender is in stock at B&H | Adorama | Amazon USA | WEX
The Canon RF 2x Extender is in stock at B&H | Adorama | Amazon USA | WEX
Rent the Canon RF 1.4x Extender and Canon RF 2x Extender from Lensrentals.