Here is a post I made back in February (do a search under PEO on the forums and you might come up with more)...you can assume that you know who our PEO was....
From personal experience, we were the client of a large PEO in Texas until the end of 2005. I was hired by my company with the express desire to pull all of our benefits/payroll/HR out of the PEO. The first thing I did when I came in was to estimate, as best I could, the cost savings. The amount I came up with was $75K annually...and that included taking into account my HR/payroll/benefits salary and assuming the highest tax and workers compensation rates. We had no more than 25 employees at any one time, so the savings was considerable at $3000 per employee. This was with keeping basically the same (or better benefits). We added STD/LTD and dropped vision coverage.
But the proof was in whether I could actually save the company that much money each year. I was able to accomplish it in 2006 AND 2007 and saved over $80K each year. And 2008 looks to be about the same ($80K over 2005 PEO prices which I am sure have only gone up). So it was very expensive for us to be in the PEO.
Some considerations:
(1) Although a lot of companies move to PEOs because they think they will get better group health or workers compensation insurance rates, we did not find that to be our case. The COBRA amounts were higher than what we were small group quoted at the time we pulled out.
(2) We found that the PEO had significant turnover and there was a different person to talk to depending on what the issue was. I had a two-sided piece of paper with names and contacts. Our "client manager" was not helpful in any knowledge -- she just passed us onto the specific group (payroll, 401k, etc)
(3) There was a lack of deep knowledge in any one area. Mistakes were made and covered up. We found quite a few when we requested records (especially on the 401k) when we pulled out. It was actually kind of scary.
(4) While they state that they assume a lot of the liability and responsibility for employment decisions, based on conversations with the DOL in late 2005, mistakes made by the PEO were considered mistakes made by the employer. Had any of our 401k participants decided to sue based on the 401k mistakes, we would have been equally liable.
(5) In most PEOs, there are specific packaged benefits. We found that there were a lot that we didn't use and no one at the PEO was reminding us they were there. For example, job descriptions and compensation surveys. Or tuition reimbursement. Things we were paying for but employees never used.
I don't ever see us returning to the world of PEOs. It would take one that had excellent knowledge and customer service skills to get me to even let them in the door to present their abilities. But I have high expectations of both myself and others. I am not their target client by any means. They were probably happy to see me go. Because I looked way below the surface and saw things that they didn't want anyone to see!
added now --- there are times when a PEO is valuable, but honestly if I were choosing a PEO, I would not consider the one you mentioned at all.