I would only recommend Jet2 if you are non rated and are planning to use it as a stepping stone to get yourself moving up the career ladder again. If you are rated I wouldn't recommended.
or (standard answer) you have seen how much worse it can be elsewhere, want to get back to the UK, want to live in the north, want to be home every night, want to have really easy winters etc etc
Are DECs hated by the current crop of remaining FOs who couldnt get into BA ?
Not so sure about the BA thing but in my time as DEC NTR I have only flown with one person who made it abundantly clear they had a problem with DEC NTR. Pretty much every other FO/SFO I have flown with have been talented people, some very experienced and more often than not a real pleasure to fly with especially when you are new on type. The big suprise to me was how many of these much more experienced on type FO's/SFO's would show real respect for you as captain and would very much want to tap into your previous airline experience on other types which for some of us is considerable.
I think quite a few SFO's at my base just can't be bothered with the difficult command procedure as it may mean a base move or failure etc so are happy to just sit tight or wait for other jobs they are applying for. Pity for the company/them but great news for people like me!