Merit has the same active ingredient (Imidacloprid).
We feel that our non-irrigated lawns will not benefit from additional fertilizer during the stressful summer months. It just isn't needed.
We have found the snapshot to work pretty well. Way back in the day we used treflan (similar to preen but more active ingredient), but it doesn't control very many weeds. Snapshot will control a lot of weeds including broadleaves. We apply the snapshot beneath the mulch to keep it from breaking down in the direct sun (it needs watered soon after application).
Lawn & Landscape Maintenance -- Landscape Installation -- Snow Management
Work / Equipment Thread