Hope I'm not too late-
BJC obviously has heard of or experienced some issues with Aerotek, as by the sounds of it have others.
I actually got my current job through them and when you bear in mind that they are in it to make money and all that goes with it, found them to be OK, although I don't know how much of that was just my recruiter who was always really helpfull.
It was a temp to perm position, my now employer was actually using them more as a recruiting firm. They'd been unable to find someone with the right combination of skills/experience and so were using aerotek to help. It was temp to begin with as a 'try before you buy' type situation. I was working for the agency for almost 7 months before I went permanent, my immediate boss & his boss wanted to make me direct sooner but internal company politics prevented this (the whole department was temporary pending proving its worth).
In my situation Aeroteks fees were based around breaking even after a year. That is if I'd contracted for a year then it wouldn't have cost my employer to take me on direct. As I went direct after only 7 months it cost them (quite a lot as I recall), had I gone direct sooner it would have cost even more. I couldn't work for my current employer for I think it was a year witout going through aerotek.
Aerotek didn't want me to even mention money with my actual boss at the company but he brought it up and ended up talking up aeroteks initial offer by a few dollars an hour to make sure he got me.
How does it affect pay/benefits, job security, etc?
Pay - in theory I got more per hour than I would have direct. In practice when I got made direct I got a small pay rise + benefits etc. however this was because I'd impressed my boss & his boss and they went to bat for me. I don't believe this is typical, as I understand it often times when you go from temp to direct you actually get a pay cut since they count benefits etc as part of your salary.
Benefits - I was eligable for healthcare through aerotech after a month or so as I recall. However it was pretty expensive so I didnt' take it up. I believe they had a 401k too but again I did't partake as it was originally only meant to be a few months. As I recall you started to earn vacation time after a certain number of hours, I think it was equivalent to about a year full time, so I never got any paid time off.
Job security - well that's something of a joke these days anyway, at least where I am. We've had some layoffs since I went direct. In theory they got rid of temps first before directs. In practice they have at least one temp still who was kept while around 20% of directs have been let go from my site in the last year or so (including unfilled positions eliminated).
As to the interview, treat it like you would any other with regards to what you wear. As such I'd expect at least shirt & tie, preferably suit.
KENAT, probably the least qualified checker you'll ever meet...