A truly beautiful if not a little unhandy book to handle in the kitchen. And that is maybe the core of what is good AND bad about this book. It looks great on the coffee table, with great photography, and insightful back ground info on the recipes, but it disappoints when one is actually trying to bake out of it.
Trying to tackle the Dalloyau's Opéra multi layer cake I ran into sloppy editing in the ingredients. For instance: according to the list you end up using 20 grams of coffee powder, whereas it is in fact 10 grams of which you hold back 10 grams after DILUTING it into water to process later. Sloppy indeed, and double the coffee taste.
In the very first paragraph, Hermé stresses to use a fat free and clean bowl and whisk to proceed with "add melted butter to the bowl" The two separate bowls of batter never come together in the description.
The amount of discrepancies in the conversions is mind boggling. I found 9 conversions to be incorrect in the ingredient list for the Opéra. Some of them were off by a considerable percentage.
It might very well be the case that a lot if not all of the recipes will work after re-adjusting and tweaking. Not being able to trust the basics will make it a less enjoyable experience though, and a bit more of a challenge.
Having said that: Even for leafing through it, reading the back stories or lusting on the pictures, this book is worth purchasing.
Conclusion: Sloppy converting set aside, this is a great book. It's a great looker on the coffee table, and baking out of it is a healthy challenge for the experienced home baker but better left for later if you're a novice.