The advantage of rope-grown mussels is that they grow clear of the seabed. That way you don't find sand or grit in them, making them much more pleasant to eat.
On holiday in Nova Scotia two years ago, saw several
beds of these mussels on a boat trip. Viewed from a distance the small markers at the head of each string
give the appearance of runway markers. Ate a great number on the boat as they are a favourite of mine.