It did take Laker at least a week or two before we knew we had a determined fellow. Determined to get out & get flying.
It is one of the things i learned right away - he needed out.
I know you have said Jerry changed when he was flighted. I think you'll see big changes once the new Budgie has the same opportunities. The first week i had Laker he'd hold onto the rope perch very hard & then beat his wings like he'd shoot to the moon if he let go. Even tho he tried to be fit for flight - he didn't have the stamina for quite a while.
I agree it will be difficult to judge him - but I think you'll know what to do. I am getting very egger to know how it goes - but don't feel too bad if you walk away - there's always the bird fair! [you can't buy them all]