This demo doesn't keep a straight 120 BPM on my machine, it's incapable of holding the rhythm after 10 seconds of playback ( I tried the first patch on the left , Edge browser).
That's unfortunate. I don't have a machine running Edge to test it on. It uses less than 20% of the CPU in Chrome on my 2012 Macbook Air. It's possible that it's a problem with my code, but in general the Web Audio API does not have very good cross-browser support.