We used them for a year and a half and they fucked up every time we added or removed an employee and everything I heard was that Paychex was just as bad.
We had employees in CA and NYC which meant ZenPayroll wasn't on the table for a while and then we switched all our HR to Trinet so it never made sense to make the switch to Zen Payroll.
I worked there about 20 years ago. Once they actually messed up, and needed to recall, all of our employee paychecks.
Our accounting department switched all of us to logging our hours using ADP EZ-labour a year ago. Since then, they've had to assign a full-time-nag who emails everyone, hounding them to do their timecards at the end of the month. She angrily admonishes everyone, telling them how at her last workplace, "everyone just did their timecard at the end of every day!" The UI is just so awful, so unforgiving of mistakes, so tedious and repetitive, that no one wants to use it.
It also wouldn't work on Firefox due to an error in the way that they were checking the current browser model, IIRC. (This was eventually fixed though)
ADP still messed up the PTO carry over hours - I think it took them 2 weeks for fix.
Or is this issue just offloaded to the customers?