Phelan of
www.parrotvolancy.com has taken Chris Biros' training course that is targeted to macaws and formulated her own recipe for flying Cockatiels.
She successfully freeflies a group of 4 Green Cheek Conure and 2 Cockatiels (also 2 Galahs but those are considered good for freeflight to most). She has attempted budgies but does not believe it is possible without a large flock.
Also Paws, Claws, and Feathers of IG freeflies two? cockatiels.
Another friend of mine freeflies a small conure that is similar in size to GCC, and ANOTHER flies Alexandrines.
Phelan is mentoring a lovebird owner for freeflight and they just recently had the first and second successful free flight. She is helping me with my BCC.
Small birds are possible, there is just an ENTIRELY different science on it - that has not been fully explored yet.
102% go with a mentor no matter what size or species you fly. But if you're going with a small species, I'd highly recommend seeking Phelan out for mentorship.
Go see FF live, and know that everything comes with freeflying. It's not to be taken lightly and is CERTAINLY not for everyone.