Yes both methods work, but mulching with leaves has a slower effect in terms of feeding, and is less smelly!
You can make a feed without smell by packing leaves tight in a bucket or pot with a hole, suspended over another bucket. Add no water. Black liquid seeps out and is odurless.
Simpler to mulch but there may then be slugs.
1. Runner Beans certainly like comfrey tea to swell pods. I believe brassicas also like it, but have not tried it out.
2. Both tomatoes and potatoes happily respond to comfrey chop n drop strategies. I have just put part of my latest cut under a pear tree, hoping that it breaks down over the next 10 weeks to support the maturing fruit.
3. Compost accelerates its formation beautifully if comfrey is added after hot composting is complete: I fill daleks with kitchen waste and top that up with initially hot composted material, cardboard, comfrey and nettles if available. It produces great stuff.
This year I am also maturing composts using biodynamic ‘balls’ containing each of the five preparations. The first maturation this spring was very quick, obviously will not know until 2020 how well things grow in it, but to touch it feels wonderful.