This is a tricky one.
I don't eat black pudding because I don't like the thought of eating blood.
However, I do eat pork, so morally I have to agree with the bi-products.
I also don't think it's any worse for you nutritionally than eating pork itself... in fact, it's possibly better for you as it wouldn't contain as much fat and would contain more iron.
So based on the above, I probably would allow Harry to eat it... but again, I couldn't eat it myself (although it's probably very tasty)