If I use a bell at all it's usually a Timber mountain bike bell that rings continuously or not at all, via a mechanical switch/damper for the clapper. Sounds kinda like an ice cream truck bell. Friendly, not too loud, seems to gently nudge folks without startling anyone. Frequency of the jingling can be roughly adjusted by tilting the bell on the handlebar, stem, frame, whatever.
Often I forget to mount a bell so I just slow as I'm overtaking folks, and in a normal voice say "Bicycle behind you," and wait for them to move. No need to holler "Onyerleft!" which causes some folks to move left. I wait for them to move whichever way they want, then pass slowly and safely around 'em. No biggie.
Mostly I avoid the MUP, other than a couple of times a month for commutes to and from group rides.
And no matter what you do, you'll encounter some MUP users who won't be happy with our choices. The MUP is like any public place. Occasionally there are some eccentric, high strung and angry folks too. Their personal issues are way beyond ringing bells or announcing an intent to pass.