After 19 years in the charter and corporate world I would say I've faired very well, particularly in regards to job security during tough times. Getting started in 2000, the poor economy meant the 121 side was slowing down. In 2001 they were shedding pilots due to furlough. Charter was the only option I had. That eventually lead me to corporate. However after a almost two decades in the "on demand" game I'm very much looking to go to the airlines. Not because of job security but simply quality of life.
To get to one of your points about a written aircraft/pay guarantee... highly unlikely. Like anywhere, progression and pay is commensurate with experience and current demand.
What other offers do you have? Regionals? If this opportunity leads to PIC time in turbine aircraft then it would serve you well. Taking this route now does not preclude an airline job for you later on down the road.