Here is the deal. I have found that my personal experience working with Trinet (I am an end user - my company oursources to them) is they are terrible. What is terrible is their back end. I have had constant problems all year with their flexible spending account. When I did a web search I found out that many of the employees there are overworked and their management it terrible. Interesting as the only good thing there is the people that answer the phone.
They bounce back a ton of flex spending - that I have never had issues with with prior companies. I highly recommend if you are looking to oursource HR and Payroll you look to another company.