What are common/traditional uses for merguez?
Favourably, we put them on the barbecue.
You can also just fry them in the pan like a chipolata.

I wouldn't eat them in combo's where you use normal sausages.
It doesn't go well with apple sauce for example.
But this is of course a question of taste.
I prefer them (when not on the BBQ) with food which doesn't contain a lot of spices, like lettuce and tomatoes with boiled potatoes.