SafoSnake collects nothing, sends nothing and has no account.
Only on the Safari tab where you turn it on, and only when you turn it on: by clicking its toolbar button or pressing Option-Shift-C. It has no permission to read any other tab or any site in the background.
The page in front of you, to lay it out in columns. That copy lives inside the tab and is gone when you close the columns. To draw the columns, SafoSnake may load the same page once more inside the tab; that request goes from your Safari to the site you are already visiting, exactly like reloading the page, and carries nothing from SafoSnake.
One setting: whether you chose Main or Full on a site, stored by Safari in the extension's own storage on this Mac, under that site's host name. Nothing else is stored, and nothing is synced.
There is no telemetry, no crash reporting of our own, no identifier and no advertising. SafoSnake makes no network requests of its own and has no server to send anything to. If macOS asks whether to share a crash report with developers, that is Apple's mechanism and your choice.