I would not use complex formulas while investing, but I also wouldn't skip a book that otherwise seems interesting because it has formulas. I'm currently about 4 chapters in McKinsey's 'Valuation' and it has some formulas too, but they just help support what they're explaining about ROIC and growth, etc. The book has make clearer some things I had been thinking about for a while about business quality, and just for that the book is already worth it.
I hope that Penman's book will similarly contain some interesting ideas that I can incorporate in my mental models even if I never use any of the formulas directly.