Each Muslim has the obligation to search all things. While it is permissible to use Tafsir as the opinion of the author, we must remember, it is not sacred writing and not the word of God(swt)
Keeping that in mind and know that until the development of photocopying, mechanical printing of Arabic was not possible. all books had to be hand copied. Many of the older Tafsir only existed in the hand written original made by the author. Once that was gone, it was gone.
Without going into detail of the difficulty in a mechanical printing: Nearly every letter has 3 different shapes depending on it's location in a word. The Pronunciation marks get even more complex and their location is based on the word.
Even with Qathir (ibn Kathir) we do not know how close to the original, today's copies are.
The Problem with the modern English language Tafsir, it might be based upon a translation, not the original Arabic.
Tafsir is a guide only and not an absolute as to what the interpretation is. Tafsir come and go, it seems everybody has an opinion.