Pros
I work with the Global Flight Training division within i3, and so cannot speak to their engineering, security and IT divisions, which comprise a significant portion of the business. However, in general, i3 has excellent leadership all the way to the top, pays very well and their corporate culture is one of integrity, virtue and strikes a very good balance between taking care of the customer AND taking care of its employees (which sometimes can be mutually exclusive.) Everyone I know who works for i3 is very happy to be there.
Cons
Within the Flight Training division, business is totally contract-dependent. When working on a contract, life is good. When not, not so good, thought the company retains you in what they call Temporary On Call status. (That's the nature of government contracting.) Naturally, one has to pay the bills. If an employee takes employment elsewhere when off contract, i3 doesn't burn bridges and will readily contact you and hire you back, if you so desire, when a new contract is put in place. The other divisions are also contract driven, but there seems to be less disruption in those divisions.