I am using speedtree, although I also have Tree It. They create the leaves by placing rectangular planes on the branches and then you have to substitute the texture of these planes with the one of the leaves that you want and mask the leaves so that is the only thing that is seen (not the surrounding of the texture). Is this better performance-wise than to model one leave and adding them all over the branches in Blender?
Generally cards (the alpha masked method) are better for performance. But with Nanite it is now possible to have individual leaves with reasonable performance. I’d recommend experimenting and profiling both for your needs.