IMO they're an "instrument of the devil" and I wouldn't use them. I didn't use them on 6 of my kids and they're all active riders- The second youngest is riding unassisted at 4 years old. The 2 y.o. is on a balance bike and she'll probably be riding a pedal bike this summer.
All without training wheels.

Balance is the skill kids need to learn- pedaling comes naturally.