So, assuming indexing would make a measurable difference on a street XK engine, who knows the optimum plug electrode orientation?
And, . . . would plugs like these negate the need for indexing.
Surface discharge plugs may or (more likely) may not make any measurable difference in performance: what the definitively do, in 2-strokes, is minimizing ‘whiskers’ across the gap that can happen on standard plugs.