Well, compared to other european battlefield, Waterloo is amazingly well preserved. Besides the huge lion hill, nothing has changed significantly. Ofc it is not 100% accurate but it is more accurate than what you could ever do by hand. Besides that you atleast get the scale right.
I would suggest using it, deleting the lion hill and making wellingtons hill slightly higher. Add the sand pit, change some roads and small hills here and there and youre done, you got a perfect waterloo map.