I will keep my review short. This is a very historic and unique place you cannot find anywhere in…read morethe world. There are different kinds of boza especially in Eastern Europe market -and I've tried many. I love Vefa the best. You can find Vefa boza in the markets all over Istanbul, but it's very fresh (and nostalgic) to get it from here.
This street has ancient specialty stores (soda-sevda gazoscusu, chickpea - tarihi vefa leblebicisi), each of them should be tried in no particular order. I am from Istanbul, I'm ashamed to not visit here very often in the past.
Bonus tip #1: Put some chickpeas on your boza. Get some chickpea cookies from the ancient cookie store nextdoor (tarihi vefa leblebicisi), they have very soft texture and go great with boza.
Bonus tip #2: Ataturk used to drink his boza here. It is written that he was making time to come and sit here- you can see his seat.
Bonus tip #3: Besides boza, they produce their own vinegar.