cost, ingredients, preparation
Kaszanka is cheaper and contains fewer ingredients. People tend to buy haggis rather than make it. Kaszanka the same - it's cheap to buy and shop bought is no different to home made.
appetising appearance, aroma, flavourfulness
Both look good, but haggis has the offal and spices which make it a richer food. Black Pudding is much closer to kaszanka. There is a sausage-shaped haggis, but this tends to be sold in fish and chip shops in some parts of Scotland. I sometimes serve haggis for dinner - Polish guests usually love it.