I like the Osterie books because I can browse the listings (as you know there are many more places mentioned than just Le Chiocciole). It is also good practice for my Italian; I think the written language is much more challenging than the spoken.
I can completely relate to the love for paper - I, too, am never without a properly-scaled paper road or trail map when we are in Italy.
For urban restaurants I just do some cross-checks, beginning maybe with Il Golosario, Trip Advisor, or even just Google Maps, then for the details go to restaurant websites and whatever guides or lists I find on the Internet (like the one from the previous post). Regional websites are sometimes helpful in promoting local businesses.
I like Il Golosario because of the good breakdown into categories. It covers also shops and producers, is constantly updated, and is searchable by region.
Since we always stay at agriturismi while in the countryside, our hosts are sometimes our best advisors in those areas.
Remember, too, that Slow Food is an organization, and not all small businesses like the politics and bureaucracy involved being under the "auspices" of a body like this. Some are fiercely independent, and others think that Slow Food is a gimmick. Still others don't care too much about catering to the niche of foreign tourists who are looking specifically, or mainly, for these "brand'-type of businesses. They have enough locals who appreciate them.
So guides/books like these are only part of the picture.
IAC, hope someone can chip in with info about the app.
I really hope you manage to make it to Italy this year - as travel re-starts we'll finally have some real-time reports on the forum, and not just tortuous reminiscing....