I like cream in my coffee....I would use butter instead simply because its hard to source grass fed cream PLUS butter keeps longer. As to the benefits. Well you get fat soluble vitamins and energy quickly.....and I freaking love coffee and cream. So thats bout it. For those that are IF'ing you eliminate insulin spikes and extend the "fast". Yes you could have eggs OR "insert food here". Really doesn't matter though. We're talking 100-200 calories of good fat.
Far as the protein deal....yes you need protein to retain lean muscle mass, however the largest determining factor is doing some resistance exercise while your in a deficit. I don't believe that anything shows that the number is anywhere near 2x body weight as protein. The guidelines in PB for .7-1g/LEAN mass is quite sufficient (I'm using lbs your using kilos so same diff ). Ketosis IS muscle sparing. It's why many use it to lean out in the bodybuilding would.
In the end BP coffee is just coffee and butter. Nothing inherently good or bad about it. And of course everyone knows its not magic.