Black pudding and its counterpart, white pudding are meat based products, made with blood and offal, fillers such as breadcrumbs and rusks, herbs, spices and other flavourings.
They are mainly a breakfast item, served as part of a fried breakfast, along with eggs, bacon, sausages etc. Different regions and areas in UK and Ireland have their own variations of the breakfast fry.
Black and white pudding may also be served in an all day breakfast or mixed grill, for lunch or dinner.
Like sausages, you can get the mass produced brands in supermarkets which have ranges from the cheap and cheerful to premium. Usually the cheaper the brand, the more fillers such as breadcrumbs are used and the flavouring , herbs and spices would be of the low quality. Then you have the fresh made in butchers and fine dining restaurants which would be made using more high quality ingredients to unique and individual recipes.
Again like sausages, peoples preference usually reflect the brand or type they can afford, and can easily buy.
In Ireland, the two most popular brands availalable to buy in supermarkerkets are
Denny Black Pudding, 199g roll costs €1.59 approx

Product details and ingredients and for the squeemish, the ingredient list is family friendly
https://www.tesco.ie/groceries/Product/Details/?id=261155273
Clonakilty Black Pudding, 280g roll costs approx €2.70

Product details and ingredients and for the squeemish, the ingredient list is family friendly
https://www.tesco.ie/groceries/Product/Details/?id=250221200
Cooking Instructions
Black pudding is sold raw, like sausages
Remove the packaging and cut into 2cm slices
Cooking Method: Grill
Place sliced pudding on a rack in a preheated grill and cook on a high heat for approximately 4 minutes on each side.
Cooking Method: Shallow Fry
Heat a small amount of oil on a frying pan and cook on a high heat for approximately 4 minutes on each side and turn occasionally.
It is not suitable for microwave cooking