Not saying it is not possible to get a flat with Marathon Plus'es, but I have found plenty of goathead's in my tire that did not cause a flat. Only one flat in many 1,000's of miles, and that was a construction staple that went into the tread (that did not cause the flat), then the other end went into the sidewall.

I find that the ride quality is fine with a B67 (spring seat) and reasonable tire pressure.