As someone who rides various places, I find them highly effective. Sure if you are on a path and a walker is using earbuds, they may not hear you. But not all walkers have the volume high. I have had some hear me just fine even when I did not expect them to hear me. The ear buds are not actually the problem. Many walkers walk in a way that is predictable. It's the ones that walk like lost fools that are dangerous. That goes for the fools on bicycles as well.

A bell riding off road on fire roads has also been very helpful. Several switchbacks on my local course so when I approach a blind turn, I ring my bell. Many times hikers coming up the opposite way know I am coming even before they see me. Many times I see them going into a formation that will avoid a collision. Some hikers are just flat out rude though. But the bell has helped me many times off road as well.

On the road? No use as there aren't any peds on the street and the cars won't hear me anyway. I just make sure I am highly visible in traffic.