Thank you! 
I agree your points are relevant concerns. :)

I think David Althaus addresses them well in his comment from another Forum post that I cite in the section Suggestions on how to implement our advice on interventions.

I intentionally tried to include details on interventions, when I found them, such that one could get an idea of whether the intervention is suited given one’s personal situation, characteristics or preferences.

But indeed, methodically trying out the recommendations seems like quite a good way to get that knowledge, as I write in the paragraph “So we suggest you adopt an open-minded and curious approach…” from the same section. The suggestion I give there to first try a Multi-component Positive Psychology intervention is inspired by this consideration, and for instance the first book and first online program I recommend for this intervention take this approach (i.e. a multi-week and relatively methodical exploration of some of the main happiness-enhancing strategies).

Thanks Gemma! I’ve slightly rephrased and pulled up the bullet point on the broad recommendations to make it clear that I also think they’re central. :)