This is the first systematic review and meta-analysis of physical activity RCTs testing mobile apps or activity trackers that enable automated and continuous self-monitoring and feedback, in adults without chronic disease. Our findings suggest that interventions using apps or trackers have small-to-moderate effects on physical activity at a mean follow-up of 13 weeks, with an average increase of 1850 steps per day, compared with control. The available evidence is of low-to-moderate quality according to the GRADE system66 and should be interpreted within the context of existing heterogeneity and publication bias. However, adjusted results accounting for the presence of publication bias remained significant… More here.
In summary it is yes. They have certainly worked for Jo and I.