Go for a J8 $.
The Nikkor is a similar design.
The Canon is similar to the Summitar in design (layout) but uses later glass and is higher contrast. The Leitz glass and coatings are soft and easier to scratch.
But mechanically and finish the Summitar is a jewel, a fondlers dream.
You will detect the Summitar will flare frequently, the Nikon almost never, but will need slooooow B&W, heavy tripod, and microscope to see other differences, and the Canon may be the best off axis on an optical chart. Without Kodachrome 25 you wount see this easily normally.
Noel