The early test versions had some real oddities with the resizing, but I see now mine show as minimised icons, and then hovering, just expands them which looks quite OK.
Live from v1.52 onwards by right-clicking on a tab and toggling the vertical tabs choice on the drop-down menu.
See
Brave browser now features vertical tabs for desktop users, maximizing on-screen space | Brave Browser#
technology #
bravebrowser 
Brave's vertical tabs feature is now available for Windows, macOS, and Linux users to experience a new way to manage open tabs.
