I've read the Spanish translation of Harry Potter as part of my attempts to read and continue learning Spanish. Starting off with the translation, yes it is indeed biased towards Latin American usage but that should in no way affect your enjoyment of the book, as long as you aware of the vosotros forms why should it? If you had learnt Spanish with Michel Thomas and books from McGraw Hill you may not even be aware of the vosotros form anyway!!
One reviewer says that the use of "ustedes" is equivalent to calling people "your graces" to Spanish ears, which is just ridiculous. Anyone at a sufficient level to be able to start reading books such as this should be aware of the differences between Peninsular and Latin American Spanish and be able to adapt without their enjoyment being spoilt. I am sure the Spanish themselves do! A book that I can recommend (although a slightly easier reading level) which liberally uses vosotros forms is the translation of Charlie And The Chocolate Factory (Charlie y la Fábrica de Chocolate) if you want some exposure.
Another criticism the same reviewer levelled at the book was the use of the English character names like "Snitch" and words like "muggles". Whilst I see his point, this did not spoil my enjoyment. Although if I had been reading aloud it would have been hard to change smoothly between English and Spanish, so I can see why he feels this way. However, the book is set in England, and therefore I personally am happy for the characters to keep their English names so I ultimately feel the decision was valid. If I was to read an English translation of a Spanish novel set in Spain I would not really want Juan to become John, and Enrique to become Henry as this would seem out of context with the setting of the book.
Aside from debate about whether this is a good resource for learning Spanish, of course the story is great. Every chapter seems to end on a note which makes it almost impossible to close the book with the intention of continuing later. As someone who has long denounced and mocked Harry Potter as "for kids" - I have not seen the films nor read the books in English - I humbly admit I was wrong!