I love the “tabs” feature, but would like to use the Yosemite look and feel. Is there a way when I open a new tab that it will now open in the existing Finder window? I know this is possible when I enable your “tabs” feature, but just curious if this possible not using the tab feature. It would be a great nice to have! 
I’m afraid I don’t follow.
If you want to use TotalFinder’s tab feature and occasionally create native Finder’s tabs, use OPT+T shortcut to open them in the same window.