Very simple and easy to use application. It is very easy to provide / check the payroll details, update timesheets, W2 / taxation details, break-down of all the pay benefits.
Easy to generate reports of the all the different entities.
The tax calculations and submission is pretty simple.
The direct deposit functionality works really well, where in you can provide the users with the ability to add multiple bank accounts in order to break the salary up.
Paychex is a promising application which has a lot of potential. The application is very easy to use for the users, you will hardly need any training before you go live with the implementation of paychex.
I have used paxchex flex for Reporting time sheets, storing the pary roll information of the employees, providing pay checks for the employees which can be later downloaded by the employees.