Design has no rules only principles - if Bembo quotes work with Adobe Garamond then go for it.

If it were English quotes “ ”, my answer might be different, but fortunately, guillemets lack identifying qualities that would match or mismatch other glyphs of a typeface. As long as you are careful to apply them consistently, it should work fine. To edit a document littered with brief font changes requires you to be mindful, lest you find you've accidentally set one whole sentence in Bembo.

To accomplish this sort of mixing, you might be best served by establishing a special character stylesheet for Bembo Book and using this for a GREP style within your basal text paragraph stylesheet to restyle all (and only) guillemets on the fly.

You should be aware that in mixing two faces like this, you will lose any kerning pairs between guillemets and adjacent letters, since the boundary will now be across fonts. Typically, the guillemets are kerned slightly with the top-heavy capitals, at the least. So, for instance, in a sequence like «Telemann» the first guillemet might not tuck so nicely in with the T as it might if set all in a single font. Depending upon the fitting of these two fonts, this may or may not present any actual visual detriment.

Thank you very much for your insights.
I didn't consider the kerning issue, so maybe I'd better to stick with Garamond alone, to avoid all risks.

In a week or so maybe I could post a couple of pages in the Critique section of this forum (or is it for fonts critique only?).

Best.

There's a "Typography/Composition" section of the Critique boards.

BTW if you have a modest budget you could have Garamond Premier modified to your taste so you don't have to switch fonts (and mess with proper kerning). I was once commissioned to add some special characters to Garamond Premier so I'm one of the many people here who could carry out such modifications for you: hpapazian at gmail dot com.

hhp