In my experience, the only silent 'buzz' is from my apple watch - and that's probably because it's not a buzz. My pebble and martian watches both had loud, obnoxious vibrations that were no better in many quiet situations than a beep would have been.

Apple's decision to put so much work in to the 'taptic engine' was a smart one IMHO - wearing any other smart watch now feels like having a moto razr strapped to my wrist when it vibrates.