God, I decided that I needed to learn the theoretical background to SAFe, and boy was I in for a surprise. In reality, it is a big Concept bingo (a bit in I had identified around 30 concepts that they tried to stuff into it, without making any coherent sense of the merger, when I thought to myself, I am only really missing three parts: Re-eningeering, Covey's 7-Habits and some crap about Tom Peters Excellence, when lo and behold Covey shows up, and about 20 pages later Tom Peters are quoted...).
SAFe is sometimes accused of being RUP (Rational Unified Process) in a new dress, but the only thing comparing this SAFe with RUP is that they are overburdened processes, that makes very little sense and which you can sell consultants for the adaptors to make it correctly (20-30 pages are assuming that you must use certified SPCs to make the concept work). It is shallow, unworkable, and incoherent, whit the added caveat in the book that if you don't adopt everything in the right way (from pair-programming in object-oriented languages) to how you set-up the enterprise mission (strategy is glossed over as something coming from God, so it will probably be addressed in later versions), etc, it will not give you the expected advantages and you need more consultant help.
This should be a funny thing, if not so many mindless IT departments hadn't adopted it as the "truth".
Many of the concepts in the framework are usable in themselves (Scrum, DevOps, OKRs, Lean, Lean Startup, Organizational Development, CI/CD, Knowledge Management, Design Thinking, Continuous Improvement, etc), but just mixing them doesn't make it a success.
The interesting part is that it manages to show modern management thinking and IT development thinking in the same framework, so that we can see what is on top of everybody's mind right now. Otherwise, avoid it and wait for the next "new" framework to show up.