Fannie's Books and Derivatives I am a bit wary of Amazon reviews so  I am asking here, are these books useful today?
useful here means; are there any objective scientific practices outlined in them that we accept today? They are not fraught with misinformation to the point where it becomes advisable to stay away from them?

(1)The Original Fannie Farmer 1896 Cook Book

(2)The Boston Cooking School Cook Book 1918

Is it better to get something derived from these books such as Fannie Farmer Baking Book 1996 by Marion Cunningham and The Fannie Farmer Cookbook Anniversary Edition September 9, 1996 by Marion Cunningham? The older books are cheaper.
"Useful" is rather subjective. If you clarify what you mean by useful I can likely clarify and improve my answer as well.

One thing to keep in mind when using old cookbooks and recipes is that terminology changes a lot over time. You may have significant difficulty translating ingredients to their modern equivalents. You also may not be able to easily find the ingredients once you do translate them. A good example is this question.

Another thing you may need to be aware of is how much our knowledge has changed. You'll likely encounter a lot more misinformation than a more modern cookbook. 

If you enjoy the extra work involved, then sure why not get the old ones. If you have trouble translating a recipe, you can always ask here! :)