If there are different schools within a field, every one of them might have a handbook (so you might have a handbook on linguistic typology, and on the other hand a handbook on generative grammar - although often the topics are even more narrow), so they still are useful to get a survey of the land even when there are different schools of thought. I also do not at all share your sense that all science is crazy antagonistic and political in the sense that "institutions discourage radical ideas" - maybe that's true of some fields, but definitely not all of them (for example, the idea makes no sense at all for mathematics). Even when different opinions and schools of thought exist that doesn't necessarily mean that there's nothing that people can agree on.

But more concretely, you can just look up the authors that contributed to the handbook and if you do indeed have a degree in the field, you'll probably recognise them and their affiliations and will be able to know (or at least look up) what tradition they belong to and what this implies for the handbook.