Less than 100 grams of mussels could give you more than 300% or the required vitamin B12, or a bit higher than 200% of manganese or 100% of selenium. Iron, iodine, C vitamin, zinc, folic acid, phosphorus make the mussel a very interesting source of nutrients.
The quality of the protein substitutes those coming from red meat with ease, so there's no reason to be guilty. At the same time it provides better fat content, avoiding saturated grease.
If the mussel is a muscle, what about our heart? With omega-3, a useful unsaturated grease, different body organs would experience benefits, like the heart. It reduces the risk of one of the most relevant causes of death surpassing a certain age.
At the same time, mussels proceed from sustainable, reasonable production methods where no damage arises from it. Perhaps, there is no better meat substitute or say source for creating an alike product that could be intermixed with it: the orange meat. The taste usually has too many adepts, so no worries in this regard.