For those who got thier 1000 121 hours at one airline as an FO, say GoJet... And then become a DEC at Endeavor.

How hard is the transition?

DEC's suck, you'd go to the bottom of the seniority list for pretty much everything

At my AA WO regional the DECs we’re somewhat resented by the training department and LCAs. Only two were good enough to make through without any hiccups I’m training that I’m aware of. The others had to redo portions of training or withdrew to fly the line as an FO for a while before trying the second time. Generally it wasn’t the aircraft/systems knowledge that did them in but it was headword/SA and failing to meet the expectations of FOM and general company knowledge

KoolJ?
filler

Let me guess, psa

Why entertain a DEC position with horrible Captain seniority when you are competitive enough to go to a ULCC/ACMI for better pay and QOL? You will still get the call from a mainline carrier going that direction….

One other thing that people don't think about is the protection part. As a new hire, you are on probation for a year. That's a year in the left seat with non to few union protections.

SkyWest has had good outcome from
street captains.. (as long as they already have time in the aircraft)

It can be a difficult transition. If they fly the same type as the previous carrier then it's hard to forget old procedures. If it is a different type then you combine learning a new aircraft while also learning a whole new company culture and policies.
In general, I see the most success from candidates with prior 121 PIC experience. Attempting it with the absolute minimum of SIC time to upgrade would generally be foolish.

Yes, it would be a real challenge with no 121. Odds are probably 50/50 at best, unless the carrier makes a very concerted effort to drag you through. Even then, a training bust or two along the way is not going to help your future job prospects.

That might depend more on the individual. If you paid attention for 1000 hours and it's on the same type that shouldn't be too difficult.

Learning somewhat different flows on the same type isn't that big of a deal if you already know systems and you "get" the airplane in question. BTDT.