I have no affiliation with Kepner-Tregoe the company, nor is that an affiliate link...
If you want to get a flavour of it the original book is pretty cheap now https://www.amazon.co.uk/Rational-Manager-Charles-Higgins-Ke...
Like I say I've tried 'em all, well nearly, KT is the only one that's worth a damn. Even the simple exercises like "is, is-not" make you feel like Poirot.
Those kinds of projects and teams have that edge over others because they have critical thinking on their side. That will benefit them first in seeing that they don't need to add a large, trademarked, expensively trained process around agile, and subsequently in remaining focused on people and code rather than process.
The commercial IBM version (RUP: Rational Unified Process) with the associated tool (rationals TM) and consulting service is really horrible though.
http://www.craiglarman.com/wiki/index.php?title=Book_Applyin...
I found its practical blending of UP with concepts traditionally associated with other processes quite illuminating.
For example, here is a snippet from section 1.1:
Iterative Development, Agile Modeling, and an Agile UP
Given many possible activities from requirements through to implementation, how should a developer or team proceed? Requirements analysis and OOA/D needs to be presented and practiced in the context of some development process. In this case, an agile (light, flexible) approach to the well-known Unified Process (UP) is used as the sample iterative development process within which these topics are introduced. However, the analysis and design topics that are covered are common to many approaches, and learning them in the context of an agile UP does not invalidate their applicability to other methods, such as Scrum, Feature-Driven Development, Lean Development, Crystal Methods, and so on.