Estimating.. How to estimate labor accurately

Hey! We are just getting started on tracking labor costs in SingleOps. As far as I can tell, there are two main ways you can track labor costs, either

1) using a Labor Item with man hours as the unit or

2) by having the crews clock in and out on visits. 

Right now we're tracking the cost using labor items with estimated labor hours. Have yall found that having the crews clock in gives more accurate labor costing?