I am a busker and I use the Peterman Grit Microphone with mounting bracket attached to my guitar for vocals. It's a great microphone with plenty of gain. All I have to compare it with is my Shure Beta 58 and I can't tell the difference, though I don't have a sound engineer's ear. No problem with feedback outside or inside. Great microphone with an obvious handmade, quality build. Will be getting another one soon, with another guitar bracket.
Just a tip. For vocals I suggest you use an SM57 wind sock with a bit of extra foam inside. It fits pretty well but I use a bit of masking tape to make it more secure. See picture.
I use a Peterman dual external acoustic guitar piezo pickup on my guitars and they are fantastic as well. Great for a natural acoustic sound and seem to need less EQing than under saddle pickups. No batteries to worry about. Very happy with my purchases.
