I have them on my bike, (the RJs version), and I don't think it damages the rear cylinder or starter.
I'm no engineer, thermal or otherwise, so I may be way off track here with my thinking.
Here is how I see it. The deflectors change the direction the heat dissapates. Heat rises, so with the deflectors, the heat rises away from your legs. It still escapes, it's just channelled forward, and away, and not to the side where your leg is. If it did trap heat to the point of causing potential damage, wouldn't the bikes go into heat management at every prolonged stop? Wouldn't engines start shutting down?
Just curious, has anybody put them on, got stuck in traffic and had the bike shut down, then pulled them off, and the bike ran okay?
I was in Las Vegas two years ago and was stuck on the strip. The bike never went into heat management, and I was so glad I had the RJ heat deflectors on my bike.
Mark