Avantages
All of my managers and the client company were fantastic. They will pay for certs. They offer internal training resources, although they're not great. Company vehicle / fuel. Friendly and experienced team leads. My particular managers showed interest in helping me advance my career and move up, taking large amounts of time out of their days to provide solid info. Fairly low oversight. As long as you're doing your job well, you won't have anyone hovering over you.
Inconvénients
The pay is at least 10% under market average. Top performers will only get a 2%-3% merit increase each year. Bonuses are solely customer sponsored, and tend to be fairly small. You generally cannot get raises if you ask due to the budget being fixed by the contract with the customer company - fairly common with MSP's. The hours were very long. At base, I would work 7 hours on site, drive 3-4 hours per day between my home and customer sites, and be paid 8 hours. This effectively, and legally, means you're making 40 hours of pay for 50+ hours out of the home, performing work-related activities. Health insurance isn't great. The only option someone in this position can afford is the HDHP.