We have a hand reared cockatiel but our new cockatiel is parent raised as we felt it will help to encourage Edmund to develop more birdie behaviours. Previously, we have always had parent raised birds or ones that were parent raised and then tamed down later on once they were independent.
I am looking forward to getting the vet appointment and results after quarantine out the way so we can begin introducing them. Although both birds have been avian vet checked and we have papers for screenings (both blood, faecal and oral) we usually get them examined after a 30 day period anyway as you should do.
The things I've noticed are:
1. The parent raised cockatiel (George) is far easier to convert to pellets, eat fresh veg and fruits or pretty much anything.
2. He's started showing his gender behaviour way sooner that Edmund did. (He was dna'd via a feather sample so we know what he is anyway)
3. Training him has been far easier than Edmund. Although Edmund was tamed when we got him the parent raised bird once hand tame is able to be far more cooperative than Edmund with flight recall etc.
4. The parent raised cockatiel is for some reason a lot bigger than Edmund at that age but that could be coincidental as all birds are different sizes and statures.
5. Oddly, George is far more cuddly than Edmund ever was. This could be a different personality but its certainly different.
6. George is way less picky about everything that Edmund. I can give him his vegetables and fruits in any way I want and he'll eat it. If I dared to give Edmund an apple that was in cubes not slices...

well... enough said
7. George shows far more natural bird behaviour like foraging and takes to new situations far faster than Edmund. In fact, he's easily friends with everyone rather than just one person bird (at least for the moment).
I think its a mixture of things that cause problems but I think hand raised birds get a distinct lack of birdy behaviour which later becomes a problem or causes problems. Hence our decision to get a parent raised companion for Edmund so he can learn to be a bird not a huma-tiel or a cock-man :p