I would say it's always worth being cautious! It's like a minefield, isn't it?! Zinc, lead, PTFE, sulpher dioxide,fungus probably many more! Coupled with breed prone's to and deficiencies, it's surprising we're not all being sped to the loony bin!!!
Pellets I would highly recommend! Cal was on parrot and cockatiel mix when the breeder handed her over and I'd read about pellets but found them hard to get? I just changed her over to good quality seed with less sunflower/junk/no dried fruit etc and fed her plenty fruit and veg. I'd already got the SD free dried fruit. I then got some pellets. Naively, I thought the breeder may have some....no. lol.
Harrisons is the best out there apparently, you can only order it from avian vets in this country as far as I'm aware. I tried Cal on zupreem which I believe is next best (no expert here AT all!!!) and she hated, I hated it because it smelt funny and it was pointless! So, she's now on Kaytee Exact which I get from ebay at a really reasonable price. They do various types for all breeds and I found their website helpful before choosing the right one for Pants. I'm sure some people would slam it but the ingredients are good on the bag, it smells HEAVENLY, so fruity, Cal loves it and as a result, eats more much needed green veg (Sun's can have vit k deficiencies - natures warferin) like spinich and kale because she's getting her "fruity" fix with the pellets.
I think between the "good" seed mix (small bag), pellets, (big bag), safe dried fruits and nuts, (medium bag) and fresh fruit/veg every day,mineral stones and cuttlefish, my girl is about as healthy as I can think to get her.
I always welcome new ideas because the day I "think I know it all" is the day I would rather be dead!
This is why I adore this forum so much. I feel that Britain as a country is very poorly equipped to care for exotic birds. The information is just not there for us to get easily!. All the pet shops I've enquired with think seed alone is fine and that's that. Such a sad idea that people must buy birds, take them home and abide by this without a second thought.
I hope that helped somehow - I am SUCH a rambler!!! xx