Hello. Firstly, thank you for utilizing the extension and sharing your feedback!
The performance bottleneck originates from the Blender API's utilization of Python to interact with the GPU module, resulting in significant time overhead. This concern prompted me to make a quality option designed to improve performance and recommend using 1 viewport sample when using the camera viewer.
Additionally, the issue of activating the camera viewer across multiple viewports is another problem that cannot be overlooked. The Blender API restricts developers from creating properties within the viewport area, thereby hindering the activation of camera viewers in specific viewports.
I hope that Blender officials consider incorporating this feature into the built-in version.
Great addon especially if you work with 2 viewports.
However this addon creates 2 console prints and I dunno how to report any bug on Gumroad.
register_class(...): Warning: 'view3d.sync_lock_view_master' does not contain 'PT' with prefix and suffix register_class(...): Warning: 'view3d.view_sync_panel' does not contain 'PT' with prefix and suffix
Thank you for the report! I'll fins a place to bug reports on future (maybe GitHub if i learn how that works haha) I fixed these issues and also made some upgrades for the addon in general. Hope you like of the new features and I'm glad that this tool is useful for you!!
Kinda great can see some use cases for that, when the camera view is in rendered mode in Eevee, it will tank performance, far more than when you use Rendered View in the normal Viewport (Tested on a Geforce 1080Ti). On Material Preview it is acceptable depending on the quality slider.
However if I use multiple viewports it activates the same camera viewer on both viewports, I hope that will get fixed so it is only on the viewport active where I enabled that feature.