I normally ride a Kawasaki KLX 250 SM and I have ridden a hand full of modern and vintage sport bikes. I recently got he chance to ride a ZERO dual sport. Honestly it was weird at first, no clutch no gear selector and no noise, it just went, and went really well. From a rolling start it would probably be faster than most 1Kcc vintage bikes, and was certainly quicker than my KLX. I did a little dirt on it as well and it performed well enough, the suspension could have been a touch better as it bottomed when I jumped it off a burm. Only real complaint I had was the steering, the stops dont allow you to steer as sharp as my KLX so low speed maneuvering would be tougher. Honestly if I had the money I would buy one in a heart beat. Also the batteries on this one lasted right about 60miles, so it would be perfect for short to medium length commutes.
I do stupid stuff, brace yourself...