Strengths: Grip, relatively lightweight and comfy.
Weaknesses: A little lack of support for distances over 20 miles on hard ground.
Overall: I run mainly over the South Downs and use Flyrocs a lot. You can really feel the ground under your feet which means you don't turn an ankle and can go faster with more confidence.
I have done two Downland marathons in them - Beachy Head and Threeforts - and my legs did feel the lack of support at those distances.